(2x+1)*(x-4)=2x^2-8x+x-4=2x^2-7x-4
(x-3)*(x+5)*(x+3)*(x-5)=(x^2-9)(x^2-25)=x^4-25x^2-9x^2+225=x^4-34x^2+225
(2x+1)*(x-4)=2x^2-8x+x-4=2x^2-7x-4
(x-3)*(x+5)*(x+3)*(x-5)=(x^2-9)(x^2-25)=x^4-25x^2-9x^2+225=x^4-34x^2+225