posted by theo .
Calculate dy/dt using the given information.
(x+y)/(x-y)= x^2 + y^2; dx/dt = 12, x = 1, y = 0
multipy both sides by (x-y)
x+y=x^3 -yx^2-xy^2-y^3 check that.
dx/dt+dy/dt= 3x^2 dx/dt-2yx dx/dt-x^2dy/dt-y^2dx/dt-3y^2 dy/dt
check that carefully, it is easy to make an error in sign.
solve for dy/dt