How to find image of a quadratic form?
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Suppose the quadratic form $f: mathbb R^3to mathbb R$ with $$f(x_1,x_2,x_3) = x_1^2 - x_2^2 - 11x_3^2 - 2x_1x_2 + 4x_1x_3 + 8x_2x_3.$$ By using Lagrange's Reduction, we have the canonical expression of $f,$ $$g(y_1,y_2,y_3) = y_1^2 - 2y_2^2 + 3y_3^2,$$ where $$y_1 = x_1 - x_2 + 2x_3,\ y_2 = x_2 - 3x_3,\ y_3 = x_3.$$ My question is: How to find the sets $f(mathbb R^3)$ and $f(mathbb R^3setminus {(0,0,0)})$ ? Thank you for your help!
linear-algebra quadratic-forms
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edited Nov 22 at 23:31