2道算式题解方程：2.3(a+5)^2-2(3-a)^2+(9-a)(9+a)=0

注意:x^=x的平方
1,原式=0.5*(x^+y^+z^+2xy+2zy+2xz)+0.5*[(x-y)^-z^]-zx-zy
=0.5(x^+y^+z^)+xy+zy+xz+0.5*(36-z^)-zx-zy
=0.5(x^+y^+z^)+xy-0.5*z^+18
=0.5(x^+y^)+xy+18
=0.5(x^+y^+2xy)+18
=0.5(x+y)^+18
根据题目,得(x-y)^=36
x^+y^-xy=36
x^+y^=78
代回去式子得0.5*(78+42)+18=78
2 3a^+75+30a-18-2a^+12a+81-a^=0
138+42a=0
21a+69=0
7a=-23
a=-23/7
自己验算..