How to evaluate $intfrac{1}{3+4x+4x^2}$?
$begingroup$
How to evaluate
$$intfrac{1}{3+4x+4x^2}quad ?
$$
This is what I've done so far:
$$
frac{1}{4} intfrac{1}{x^2+x+frac{3}{4}}
=frac{1}{4} intfrac{1}{(x+frac{1}{2})^2 + frac{1}{2}}
$$
$$
y = frac{1}{a}arctanfrac{u}{a},quad frac{dy}{du} = frac{1}{a^2 + u^2}
$$
$$
a = sqrt{frac{1}{2}},quad
u = (x+frac{1}{2}),quad frac{du}{dx} = 1
$$
so
$$ frac{dy}{dx} = frac{dy}{du} cdot 1
$$
I don't know how to proceed.
Could I also have some help with
$$
intfrac{1}{sqrt{-4x^2-4x+3}}quad ?
$$
calculus integration
$endgroup$
|
show 1 more comment
$begingroup$
How to evaluate
$$intfrac{1}{3+4x+4x^2}quad ?
$$
This is what I've done so far:
$$
frac{1}{4} intfrac{1}{x^2+x+frac{3}{4}}
=frac{1}{4} intfrac{1}{(x+frac{1}{2})^2 + frac{1}{2}}
$$
$$
y = frac{1}{a}arctanfrac{u}{a},quad frac{dy}{du} = frac{1}{a^2 + u^2}
$$
$$
a = sqrt{frac{1}{2}},quad
u = (x+frac{1}{2}),quad frac{du}{dx} = 1
$$
so
$$ frac{dy}{dx} = frac{dy}{du} cdot 1
$$
I don't know how to proceed.
Could I also have some help with
$$
intfrac{1}{sqrt{-4x^2-4x+3}}quad ?
$$
calculus integration
$endgroup$
$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
1
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21
|
show 1 more comment
$begingroup$
How to evaluate
$$intfrac{1}{3+4x+4x^2}quad ?
$$
This is what I've done so far:
$$
frac{1}{4} intfrac{1}{x^2+x+frac{3}{4}}
=frac{1}{4} intfrac{1}{(x+frac{1}{2})^2 + frac{1}{2}}
$$
$$
y = frac{1}{a}arctanfrac{u}{a},quad frac{dy}{du} = frac{1}{a^2 + u^2}
$$
$$
a = sqrt{frac{1}{2}},quad
u = (x+frac{1}{2}),quad frac{du}{dx} = 1
$$
so
$$ frac{dy}{dx} = frac{dy}{du} cdot 1
$$
I don't know how to proceed.
Could I also have some help with
$$
intfrac{1}{sqrt{-4x^2-4x+3}}quad ?
$$
calculus integration
$endgroup$
How to evaluate
$$intfrac{1}{3+4x+4x^2}quad ?
$$
This is what I've done so far:
$$
frac{1}{4} intfrac{1}{x^2+x+frac{3}{4}}
=frac{1}{4} intfrac{1}{(x+frac{1}{2})^2 + frac{1}{2}}
$$
$$
y = frac{1}{a}arctanfrac{u}{a},quad frac{dy}{du} = frac{1}{a^2 + u^2}
$$
$$
a = sqrt{frac{1}{2}},quad
u = (x+frac{1}{2}),quad frac{du}{dx} = 1
$$
so
$$ frac{dy}{dx} = frac{dy}{du} cdot 1
$$
I don't know how to proceed.
Could I also have some help with
$$
intfrac{1}{sqrt{-4x^2-4x+3}}quad ?
$$
calculus integration
calculus integration
edited Dec 10 '18 at 3:35
user587192
1
1
asked Dec 10 '18 at 1:02
YeeetYeeet
133
133
$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
1
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21
|
show 1 more comment
$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
1
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21
$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
1
1
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21
|
show 1 more comment
2 Answers
2
active
oldest
votes
$begingroup$
What can be done is a double U-Substitution
We have $$intfrac{1}{3+4x+4x^2}dx$$
By completing the square we see $$intfrac{1}{3+4x+4x^2}dx = intfrac{1}{(2x+1)^2+2}dx$$
Now substitute $u = 2x+1$ and $du = 2udx$. Now our integral becomes $$frac{1}{2}intfrac{1}{u^2+2}du = frac{1}{2}intfrac{1}{2(frac{u^2}{2}+1)}du = frac{1}{4}intfrac{1}{(frac{u^2}{2}+1)}du$$
Now we substitute $s = frac{u}{sqrt{2}}$ and $ds = frac{1}{sqrt{2}}du$
in the integrand. $$frac{1}{2sqrt{2}}intfrac{1}{s^2+1}ds$$
$$intfrac{1}{s^2+1}ds = tan^{-1}(s)$$ So we are left with $$frac{tan^{-1}(s)}{2sqrt{2}}$$
Back substituting $s = frac{u}{sqrt{2}}$, $$frac{tan^{-1}(s)}{2sqrt{2}} = frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}}$$
Now back substitute $u = 2x+1$ and $$frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}} = frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}$$,
so our final answer is $$boxed{frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}+ C}$$
$endgroup$
add a comment |
$begingroup$
HINT:Complete the squares and use the results
$$intfrac{1}{x^2 + a^2}dx= frac{1}{a}arctan frac{x}{a}+C $$
and
$$intfrac{1}{sqrt{a^2-x^2}}dx=arcsin frac{x}{a}+C$$.
$endgroup$
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
What can be done is a double U-Substitution
We have $$intfrac{1}{3+4x+4x^2}dx$$
By completing the square we see $$intfrac{1}{3+4x+4x^2}dx = intfrac{1}{(2x+1)^2+2}dx$$
Now substitute $u = 2x+1$ and $du = 2udx$. Now our integral becomes $$frac{1}{2}intfrac{1}{u^2+2}du = frac{1}{2}intfrac{1}{2(frac{u^2}{2}+1)}du = frac{1}{4}intfrac{1}{(frac{u^2}{2}+1)}du$$
Now we substitute $s = frac{u}{sqrt{2}}$ and $ds = frac{1}{sqrt{2}}du$
in the integrand. $$frac{1}{2sqrt{2}}intfrac{1}{s^2+1}ds$$
$$intfrac{1}{s^2+1}ds = tan^{-1}(s)$$ So we are left with $$frac{tan^{-1}(s)}{2sqrt{2}}$$
Back substituting $s = frac{u}{sqrt{2}}$, $$frac{tan^{-1}(s)}{2sqrt{2}} = frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}}$$
Now back substitute $u = 2x+1$ and $$frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}} = frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}$$,
so our final answer is $$boxed{frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}+ C}$$
$endgroup$
add a comment |
$begingroup$
What can be done is a double U-Substitution
We have $$intfrac{1}{3+4x+4x^2}dx$$
By completing the square we see $$intfrac{1}{3+4x+4x^2}dx = intfrac{1}{(2x+1)^2+2}dx$$
Now substitute $u = 2x+1$ and $du = 2udx$. Now our integral becomes $$frac{1}{2}intfrac{1}{u^2+2}du = frac{1}{2}intfrac{1}{2(frac{u^2}{2}+1)}du = frac{1}{4}intfrac{1}{(frac{u^2}{2}+1)}du$$
Now we substitute $s = frac{u}{sqrt{2}}$ and $ds = frac{1}{sqrt{2}}du$
in the integrand. $$frac{1}{2sqrt{2}}intfrac{1}{s^2+1}ds$$
$$intfrac{1}{s^2+1}ds = tan^{-1}(s)$$ So we are left with $$frac{tan^{-1}(s)}{2sqrt{2}}$$
Back substituting $s = frac{u}{sqrt{2}}$, $$frac{tan^{-1}(s)}{2sqrt{2}} = frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}}$$
Now back substitute $u = 2x+1$ and $$frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}} = frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}$$,
so our final answer is $$boxed{frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}+ C}$$
$endgroup$
add a comment |
$begingroup$
What can be done is a double U-Substitution
We have $$intfrac{1}{3+4x+4x^2}dx$$
By completing the square we see $$intfrac{1}{3+4x+4x^2}dx = intfrac{1}{(2x+1)^2+2}dx$$
Now substitute $u = 2x+1$ and $du = 2udx$. Now our integral becomes $$frac{1}{2}intfrac{1}{u^2+2}du = frac{1}{2}intfrac{1}{2(frac{u^2}{2}+1)}du = frac{1}{4}intfrac{1}{(frac{u^2}{2}+1)}du$$
Now we substitute $s = frac{u}{sqrt{2}}$ and $ds = frac{1}{sqrt{2}}du$
in the integrand. $$frac{1}{2sqrt{2}}intfrac{1}{s^2+1}ds$$
$$intfrac{1}{s^2+1}ds = tan^{-1}(s)$$ So we are left with $$frac{tan^{-1}(s)}{2sqrt{2}}$$
Back substituting $s = frac{u}{sqrt{2}}$, $$frac{tan^{-1}(s)}{2sqrt{2}} = frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}}$$
Now back substitute $u = 2x+1$ and $$frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}} = frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}$$,
so our final answer is $$boxed{frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}+ C}$$
$endgroup$
What can be done is a double U-Substitution
We have $$intfrac{1}{3+4x+4x^2}dx$$
By completing the square we see $$intfrac{1}{3+4x+4x^2}dx = intfrac{1}{(2x+1)^2+2}dx$$
Now substitute $u = 2x+1$ and $du = 2udx$. Now our integral becomes $$frac{1}{2}intfrac{1}{u^2+2}du = frac{1}{2}intfrac{1}{2(frac{u^2}{2}+1)}du = frac{1}{4}intfrac{1}{(frac{u^2}{2}+1)}du$$
Now we substitute $s = frac{u}{sqrt{2}}$ and $ds = frac{1}{sqrt{2}}du$
in the integrand. $$frac{1}{2sqrt{2}}intfrac{1}{s^2+1}ds$$
$$intfrac{1}{s^2+1}ds = tan^{-1}(s)$$ So we are left with $$frac{tan^{-1}(s)}{2sqrt{2}}$$
Back substituting $s = frac{u}{sqrt{2}}$, $$frac{tan^{-1}(s)}{2sqrt{2}} = frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}}$$
Now back substitute $u = 2x+1$ and $$frac{tan^{-1}(frac{u}{sqrt{2}})}{2sqrt{2}} = frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}$$,
so our final answer is $$boxed{frac{tan^{-1}(frac{2x+1}{sqrt{2}})}{2sqrt{2}}+ C}$$
answered Dec 10 '18 at 1:29
Aniruddh VenkatesanAniruddh Venkatesan
149112
149112
add a comment |
add a comment |
$begingroup$
HINT:Complete the squares and use the results
$$intfrac{1}{x^2 + a^2}dx= frac{1}{a}arctan frac{x}{a}+C $$
and
$$intfrac{1}{sqrt{a^2-x^2}}dx=arcsin frac{x}{a}+C$$.
$endgroup$
add a comment |
$begingroup$
HINT:Complete the squares and use the results
$$intfrac{1}{x^2 + a^2}dx= frac{1}{a}arctan frac{x}{a}+C $$
and
$$intfrac{1}{sqrt{a^2-x^2}}dx=arcsin frac{x}{a}+C$$.
$endgroup$
add a comment |
$begingroup$
HINT:Complete the squares and use the results
$$intfrac{1}{x^2 + a^2}dx= frac{1}{a}arctan frac{x}{a}+C $$
and
$$intfrac{1}{sqrt{a^2-x^2}}dx=arcsin frac{x}{a}+C$$.
$endgroup$
HINT:Complete the squares and use the results
$$intfrac{1}{x^2 + a^2}dx= frac{1}{a}arctan frac{x}{a}+C $$
and
$$intfrac{1}{sqrt{a^2-x^2}}dx=arcsin frac{x}{a}+C$$.
answered Dec 10 '18 at 1:31
Thomas ShelbyThomas Shelby
3,3271524
3,3271524
add a comment |
add a comment |
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$begingroup$
$$ x^2 + x + frac{3}{4} = left( x + frac{1}{2} right)^2 + frac{1}{2} $$
$endgroup$
– Will Jagy
Dec 10 '18 at 1:07
$begingroup$
Unrelated note: remember to add a $dx$ at the end of your integrals.
$endgroup$
– YiFan
Dec 10 '18 at 1:10
$begingroup$
Fixed. Thanks for pointing it out
$endgroup$
– Yeeet
Dec 10 '18 at 1:10
$begingroup$
so is the answer $$frac{sqrt2}{4}arctansqrt2({x+frac{1}{2}})$$?
$endgroup$
– Yeeet
Dec 10 '18 at 1:20
1
$begingroup$
If you want to check the answer, try going to Wolfram Alpha, which can basically calculate everything for you.
$endgroup$
– YiFan
Dec 10 '18 at 1:21