Question

5(5x-3y)^2-20(3x-2y)^2

Answer 1

(a-b)^2=a^2+b^2-2ab
(5x-3y)^2=25x^2+9y^2-30xy
(3x-2y)^2=9x^2+4y^2-12xy
[5(25x^2+9y^2-30xy)]-[20(9x^2+4y^2-12xy)]
=125x^2+45y^2-150xy-180x^2-80y^2+240xy
=-55x^2-35y^2+90xy