Question

先化简，再求值：5xy^2-[3xy^2-(4xy^2-2x^2y)]+2x^2y-xy^2,其中x=-4，y=二分之一

Answer 1

当x=-4，y=1/2时
5xy^2-[3xy^2-(4xy^2-2x^2y)]+2x^2y-xy^2
= 5xy²-3xy²+4xy²-2x²y+2x²y-xy²
=5xy²=5×(-4)×(1/2)²=-5

Answer 2

5xy^2-[3xy^2-(4xy^2-2x^2y)]+2x^2y-xy^2
=5xy^2-(3xy^2-4xy^2+2x^2y)+2x^2y-xy^2
=5xy^2-3xy^2+4xy^2-2x^2y+2x^2y-xy^2
=(5-3+4-1)xy^2+(-2+2)x^2y
=5xy^2
=5*(-4)*(二分之一)^2
=5*(-4)*(四分之一)
=5*(-1)
=-5