1.已知a+b=3,求a的平方-b的平方+6b的值
a²-b²+6b
=(a+b)(a-b)+6b
=3(a-b)+6b
=3(a+b)
=9
2.已知（x+y）的平方=25,求（2x+2y-1）（2x+2y+1）的值
(2x+2y-1)(2x+2y+1)
=4(x+y)²-1
=100-1
=99