运用乘法公式

(x+y+1)(x+y-1)
=[(x+y)+1]*[(x+y)-1]
=(x+y)^2-1
=x^2+2xy+y^2-1
(2x-y-3)²
=[(2x-y)-3]^2
=(2x-y)^2-9
=4x^2-4xy+y^2-9
(2x-y-3)³
同上题
【（x+2）（x-2）】²
=[x^2-4]^2
=x^4-8x^2+16
(2x+3y)²-(2x+y)(2x-y)
=4x^2+12xy+9y^2-4x^2+y^2
=12xy+10y^2
=12*1/3*(-1/2)+10*(-1/2)^2
=-2+2.5
=0.5