Finding range of $a$
$begingroup$
If $$f(x) =
begin{cases}
|x-2|+a^2-9a-9, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$ has local minima at $x=2$, then range of $a$ is… ?
My failed Attempt:
Wrote
$$f(x) =
begin{cases}
-x+a^2-9a-7, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$
The problem here is that I don't know whether the function is continious is required or not for finding maxima and minima. Not that I could check it if it was
Then My next step would be differentiating
$$f(x) =
begin{cases}
-1, &text{if }x<2\
2, &text{if } xgeqslant2
end{cases}$$
That means the function is decreasing before $x=2$ and then increasing. This is the best I could think for this question but it's not providing me any hint on how to proceed
calculus
$endgroup$
add a comment |
$begingroup$
If $$f(x) =
begin{cases}
|x-2|+a^2-9a-9, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$ has local minima at $x=2$, then range of $a$ is… ?
My failed Attempt:
Wrote
$$f(x) =
begin{cases}
-x+a^2-9a-7, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$
The problem here is that I don't know whether the function is continious is required or not for finding maxima and minima. Not that I could check it if it was
Then My next step would be differentiating
$$f(x) =
begin{cases}
-1, &text{if }x<2\
2, &text{if } xgeqslant2
end{cases}$$
That means the function is decreasing before $x=2$ and then increasing. This is the best I could think for this question but it's not providing me any hint on how to proceed
calculus
$endgroup$
$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
2
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41
add a comment |
$begingroup$
If $$f(x) =
begin{cases}
|x-2|+a^2-9a-9, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$ has local minima at $x=2$, then range of $a$ is… ?
My failed Attempt:
Wrote
$$f(x) =
begin{cases}
-x+a^2-9a-7, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$
The problem here is that I don't know whether the function is continious is required or not for finding maxima and minima. Not that I could check it if it was
Then My next step would be differentiating
$$f(x) =
begin{cases}
-1, &text{if }x<2\
2, &text{if } xgeqslant2
end{cases}$$
That means the function is decreasing before $x=2$ and then increasing. This is the best I could think for this question but it's not providing me any hint on how to proceed
calculus
$endgroup$
If $$f(x) =
begin{cases}
|x-2|+a^2-9a-9, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$ has local minima at $x=2$, then range of $a$ is… ?
My failed Attempt:
Wrote
$$f(x) =
begin{cases}
-x+a^2-9a-7, &text{if }x<2\
2x-3, &text{if } xgeqslant2
end{cases}$$
The problem here is that I don't know whether the function is continious is required or not for finding maxima and minima. Not that I could check it if it was
Then My next step would be differentiating
$$f(x) =
begin{cases}
-1, &text{if }x<2\
2, &text{if } xgeqslant2
end{cases}$$
That means the function is decreasing before $x=2$ and then increasing. This is the best I could think for this question but it's not providing me any hint on how to proceed
calculus
calculus
edited Jan 27 at 15:02
Zerix
asked Sep 24 '18 at 10:26
ZerixZerix
1378
1378
$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
2
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41
add a comment |
$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
2
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41
$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
2
2
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
A non-continuous function can also have the minimum at $x=2$
Here you want a local minimum at $x=2$ thus
$$
|2-2|+a^2-9a-9ge 2cdot2-3
$$
$$
a^2-9a-9ge 1
$$
$$(a+1)(a-10)ge 0$$
You get $$ain(-infty,-1]cup[10,infty)$$
You can look here on desmos for the simulation
$endgroup$
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
add a comment |
$begingroup$
There's no other way of doing this question except assuming it is continuous, otherwise why would they have given you the function broken like this at x=2?
So, put right hand limit and you get 4-3=1.
Put x=2 for x<2 to get $a^2$-9a-9.
Since the function is continuous, both limits will be same, i.e. 1
So, $$a^2-9a-9=1$$ $$ a^2-9a-10=0 $$
$$(a-10)(a+1)=0 $$
$$a=10$$ or $$a=-1$$
$endgroup$
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
add a comment |
Your Answer
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
A non-continuous function can also have the minimum at $x=2$
Here you want a local minimum at $x=2$ thus
$$
|2-2|+a^2-9a-9ge 2cdot2-3
$$
$$
a^2-9a-9ge 1
$$
$$(a+1)(a-10)ge 0$$
You get $$ain(-infty,-1]cup[10,infty)$$
You can look here on desmos for the simulation
$endgroup$
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
add a comment |
$begingroup$
A non-continuous function can also have the minimum at $x=2$
Here you want a local minimum at $x=2$ thus
$$
|2-2|+a^2-9a-9ge 2cdot2-3
$$
$$
a^2-9a-9ge 1
$$
$$(a+1)(a-10)ge 0$$
You get $$ain(-infty,-1]cup[10,infty)$$
You can look here on desmos for the simulation
$endgroup$
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
add a comment |
$begingroup$
A non-continuous function can also have the minimum at $x=2$
Here you want a local minimum at $x=2$ thus
$$
|2-2|+a^2-9a-9ge 2cdot2-3
$$
$$
a^2-9a-9ge 1
$$
$$(a+1)(a-10)ge 0$$
You get $$ain(-infty,-1]cup[10,infty)$$
You can look here on desmos for the simulation
$endgroup$
A non-continuous function can also have the minimum at $x=2$
Here you want a local minimum at $x=2$ thus
$$
|2-2|+a^2-9a-9ge 2cdot2-3
$$
$$
a^2-9a-9ge 1
$$
$$(a+1)(a-10)ge 0$$
You get $$ain(-infty,-1]cup[10,infty)$$
You can look here on desmos for the simulation
edited Sep 24 '18 at 13:25
answered Sep 24 '18 at 12:46
Deepesh MeenaDeepesh Meena
4,30421025
4,30421025
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
add a comment |
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
$begingroup$
Can you tell me what did you do..... I am unable to. Understand it. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 14:11
add a comment |
$begingroup$
There's no other way of doing this question except assuming it is continuous, otherwise why would they have given you the function broken like this at x=2?
So, put right hand limit and you get 4-3=1.
Put x=2 for x<2 to get $a^2$-9a-9.
Since the function is continuous, both limits will be same, i.e. 1
So, $$a^2-9a-9=1$$ $$ a^2-9a-10=0 $$
$$(a-10)(a+1)=0 $$
$$a=10$$ or $$a=-1$$
$endgroup$
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
add a comment |
$begingroup$
There's no other way of doing this question except assuming it is continuous, otherwise why would they have given you the function broken like this at x=2?
So, put right hand limit and you get 4-3=1.
Put x=2 for x<2 to get $a^2$-9a-9.
Since the function is continuous, both limits will be same, i.e. 1
So, $$a^2-9a-9=1$$ $$ a^2-9a-10=0 $$
$$(a-10)(a+1)=0 $$
$$a=10$$ or $$a=-1$$
$endgroup$
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
add a comment |
$begingroup$
There's no other way of doing this question except assuming it is continuous, otherwise why would they have given you the function broken like this at x=2?
So, put right hand limit and you get 4-3=1.
Put x=2 for x<2 to get $a^2$-9a-9.
Since the function is continuous, both limits will be same, i.e. 1
So, $$a^2-9a-9=1$$ $$ a^2-9a-10=0 $$
$$(a-10)(a+1)=0 $$
$$a=10$$ or $$a=-1$$
$endgroup$
There's no other way of doing this question except assuming it is continuous, otherwise why would they have given you the function broken like this at x=2?
So, put right hand limit and you get 4-3=1.
Put x=2 for x<2 to get $a^2$-9a-9.
Since the function is continuous, both limits will be same, i.e. 1
So, $$a^2-9a-9=1$$ $$ a^2-9a-10=0 $$
$$(a-10)(a+1)=0 $$
$$a=10$$ or $$a=-1$$
answered Sep 24 '18 at 11:01
ideaidea
2,16841125
2,16841125
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
add a comment |
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
If I substitute a=-2 in the question then I get -x+15.This gives decreasing till 2 then increasing making x=2 minima I guess so I don't think x=-1 is the only solution. And the question also asks about range
$endgroup$
– Zerix
Sep 24 '18 at 11:08
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
a=10 and a=-1 are the 2 solutions.There are discrete values and not the range for a. And, given function needs to be decreasing and then increasing if it has to be continuous.
$endgroup$
– idea
Sep 24 '18 at 11:27
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
$begingroup$
you solution is partially correct look at my solution hope you understand
$endgroup$
– Deepesh Meena
Sep 24 '18 at 12:58
add a comment |
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$begingroup$
A non-continuous function can also have (local) extrema.
$endgroup$
– Karlo
Sep 24 '18 at 10:34
$begingroup$
I always get confused at non continious functions. I haven't seen examples of them so that's why I am always little confused when dealing with them
$endgroup$
– Zerix
Sep 24 '18 at 10:36
2
$begingroup$
Should it be $|x-2|$ in the task? Otherwise I do not see how you get to $-x$ in the next step.
$endgroup$
– Florian
Sep 24 '18 at 10:38
$begingroup$
I miswrote that when double checked with my textbook. Sorry for the inconvenience
$endgroup$
– Zerix
Sep 24 '18 at 10:41