1.运用乘法公式计算:
⑴(3x-5)的平方-(2x+7)的平方
=（3x-5+2x+7)(3x-5-2x-7)
=(5x+2)(x-12)
=5x^2 -58x-24
⑵(x+y+1)(x+y-1)
=(x+y)^2-1
=x^2 + y^2 + 2xy - 1
⑶(2x-y-3)的平方
=4x^2-4x(y+3)+(y+3)^2
=4x^2 - 4xy -12 + y^2 + 6y + 9
=4x^2 + y^2 - 4xy + 6y - 3
⑷[(x+2)(x-2)]的平方
=(x^2-4)^2
=x^4 - 8x^2 +1 6
2.(2x+3y)^2-(2x+y)(2x-y),其中x=1/3,y=-1/2
(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+5/2
=1/2