Here's the question you clicked on:
edr1c
(a) Find an orthogonal matrix which will transform the quadratic form Q=5x^2 +8y^2 -4xy into sum of squares (b) Reduce the conic 5x^2 +8y^2 -4xy -36 = 0 into standard form (sum of squares) and sketch the conic.
for b, group like terms (get all the x's together and all the y's together).
I'm trying to remember how to do part. a. Lol But I think you use the 1,0,0: 0,1,0, 0,0,1 matrix set to find it's orthogonality.