(x^2+y^2)(a^2-b^2)-(xa+yb)^2

Question

(x^2+y^2)(a^2-b^2)-(xa+yb)^2

Answer 1

(x²+y²)(a²-b²)-(x a+yb)² = x²a²-x²b²+y²a²-y²b²- x²a²-2xayb-y²b² = -x² b²+y²a²-2y²b²-2xayb