1.(3a+b)^-（3a-b)^
=(3a+b+3a-b)(3a+b-3a+b)
=6a*2b
=12ab
2.79.8^
=(80-0.2)^
=6400-32+0.04
=6368.04
3.解方程：(x-1)(x-2)+(x-2)（x+2）=2（x-3）(x+3)-2
(x-2)(2x+1)=2x^2-18-2
2x^2-3x-2=2x^2-18-2
3x=18
x=6
4.先化简,再求值:
(1).y（x+y）+(x+y)(x-y)-x^,其中x=-2,y=二分之一
=x(x+y)-x^
=xy
=-1
(2).x^+y^=50,x+y=10.求xy的值
2xy=(x+y)^-(x^2+y^2)
=100-50
=50
xy=25