这个是要解方程吧
3(x+5)^2-2(x+3)^2-(x-9)(x+9)=81
3(x^2+10x+25)-2(x^2+6x+9)-x^2+81=81
3x^2+30x+75-2x^2-12x-18-x^2=0
18x+57=0
x=-19/6