(X+5y)(x+4y)-(x-5y)(x+5y),其中x=3,y=-1/3化简求值

问题描述:

(X+5y)(x+4y)-(x-5y)(x+5y),其中x=3,y=-1/3化简求值

原式=x^2+9xy+20y^2-(x^2-25y^2)
=9xy+45y^2
把x=3,y=-1/3
原式=-9+45*1/9=-4