Sorry for a stupid question, just haven't dealt with maths

>>7795863
Did you ever learn how to do plane rotations?

>>7795870
yea.. which was quite some time ago..

>>7795863
Im thinking definite integral and playing around with sinhx and coshx maybe?

anyone?

replace y with (x+y)/sqrt(2) and y with (x-y)/sqrt(2)
use these new variables

>>7795935
can you explain the reasoning? what is the full formula with cos and sin?

>>7796006
x= xcos theta - y costheta
y = x sintheta + y cos(theta)

or something like that. Look up quadratic forms (matrices) and rotations of (x, y) column vectors.

The formula for what you have is z = Tranpose(v) tranpose(R) [1/a^2 0 0 -1/b^2] R v

where v is [x y] in column form and R is your rotation matrix and [1/a^2 0 0 -1/b^2] is an obvious 2x2 Matrix.