Question

r^4-4s^4

can someone show me how i get (r^2+2s^2) (r^2-2s^2)??

Answer 1

reverse foil. in the second equation, r^2 * r^2= r^4, in the back, 2s^2 * (-2)s^2, it is (-4)s^4, the (r^2)(2s^2)-(r^2)(2s^2) cancel each other, leaving r^4-4s^4