How do you graph y² - x² - 2y + 4x - 4 =0?

1 Answer
Jul 11, 2016

A hyperbole

h(x,y)=1/2{x-2,y-1}((-2,0),(0,2)){x-2,y-1}-1

Explanation:

f(x,y) = y² - x² - 2y + 4x - 4 =0 is a conic

The kind of conic can be answered after analyzing its associated quadratic form.

q_f(x,y) =1/2 {x,y}((f_{x x},f_{x y}),(f_{y x},f_{y y})){x,y}

where f_{x_1,x_2} =( partial^2f)/(partial x_1 partial x_2)

Here

((f_{x x},f_{x y}),(f_{y x},f_{y y}))=((-2,0),(0,2)) with eigenvalues {-2,2} which characterize this conic as a Hyperbole.

The hyperbole canonic representation is

h(x,y)=1/2{x-x_0,y-y_0}((-2,0),(0,2)){x-x_0,y-y_0}+c_0

Now, comparing

f(x,y)=h(x,y) we obtain the conditions:

{ (x_0^2 - y_0^2-4-c_0 = 0), (2 y_0-2 = 0), (4 - 2 x_0 =0) :}

Solving for x_0,y_0,c_0 gives

{x_0 = 2, y_0 = 1, c_0 = -1}

so the hyperbole is

h(x,y)=1/2{x-2,y-1}((-2,0),(0,2)){x-2,y-1}-1

centered at {2,1}

(y-1)^2-(x-2)^2-1=0->(y-x+1)(y+x-3)-1=0

so the assymptotes are

y-x+1=0 and y+x-3=0

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