化简求值:3(x-2y)(1/3x+2/3y),其中x=1,y=-1/2?求得(要过程)

问题描述:

化简求值:3(x-2y)(1/3x+2/3y),其中x=1,y=-1/2?求得(要过程)

3(x-2y)(1/3x+2/3y)
=(x-2y)(x+2y)
=x^2-4y^2
=1^2-4*(-1/2)^2
=1-1=0