题目

x^2-y^2分之2x^2+3xy+y^2乘2x-y分之5x+5y其中x=-2,y=3?先化简再求值

提问时间：2021-03-20

答案

[(2x²+3xy+y²)/(x²-y²)][(5x+5y)/(2x-y)]
=[(x+y)(2x+y)/(x+y)(x-y)][5(x+y)/(2x-y)]
=[(2x+y)/(x-y)][5(x+y)/(2x-y)]
=5(2x+y)(x+y)/[(x-y)(2x-y)]
=5[2×(-2)+3](-2+3)/[(-2-3)[2×(-2)-3]]
=5×(-1)×1/[(-5)×(-7)]
=-5/35
=-1/7