Question

(4x—y)(3x+2y)-5x(3x+y)其中x=二分之一

(3x+2y)(4x-5y)-11(x+y)(x-y)+5xy,其中x＝三分之一,y＝-二分之一.
先化简再求值.

Answer 1

原式
12x²+8xy-15xy-10y²-11(x²-y²)+5xy
=12x²-7xy-10y²-11x²+11y²+5xy
=x²+y²-2xy
=(x-y)²
将x=1/3
y=-1/2
代入（1/3+1/2)²
=(5/6)²
=25/36