1. Apr 7, 2006

### stunner5000pt

Write the equation in terms of new caraibles so that it is in standard position and identify the curve

$$3x^2 - 4xy = 2$$

here a = 3, b = -4, c = 0 , $$d = \sqrt{(-4)^2+(3-0)^2} = 5 [/itex] [tex] \cos\theta = \frac{a+c-d}{\sqrt{b^2 + (a+c-d)^2}} = \frac{-2}{2\sqrt{5}}$$
$$\sin\theta = \frac{b}{\sqrt{b^2 + (a+c-d)^2}} = \frac{4}{\sqrt{20}}$$

so $$P = \frac{1}{\sqrt{5}} \left(\begin{array}{cc} -1&-2 \\ 2&-1 \end{array}\right)$$

from X = PY i get
$$x = \frac{-1}{\sqrt{5}} (x_{1}-2y_{1})$$
$$y = \frac{-1}{\sqrt{5}} (2x_{1}+y_{1})$$
where x1 and y1 are the new variables
is this fine??

is this how you get the change of variables??