4(x²-y)(x²+y)-(2x²-y)²,其中x=2,y=-5.这是因式分解的化简求值要过程速度.

4(x²-y)(x²+y)-(2x²-y)²
＝4x^4-4y^2-4x^4+4x^2y-y^2
=4x^2y-5y^2
=y(4x^2-5y)
=-5(4*2*2-5*(-5))
=-5(16+25)
=-80-125
=-20512x²（y+2)-36x（y+2)，其中x=2，y=212x²（y+2)-36x（y+2)=12x(xy+2x-3y-6)=48(4+4-6-6)=-192