（-2ab²)^3×（3a²b)²+4a^3b²×18a^4b^6
=-8a^3b^6×9a^4b^2+4a^3b²×18a^4b^6
=-72a^(3+4)b^(6+2)+72a^(3+4)b(2+6)
=-72a^7b^8+72a^7b^8
=0
1/2(x+y+z)^2+1/2(x-y-z)(x-y+z)-z(x+y)
=[(x+y)^2+2z(x+y)+z^2]/2+[(x-y)^2-z^2]/2-[2z(x+y)]/2
=[(x+y)^2+2z(x+y)+z^2+(x-y)^2-z^2-2z(x+y)]/2
=[(x+y)^2+(x-y)^2]/2
=[x^2+y^2+2xy+(x-y)^2]/2
=[x^2+y^2-2xy+4xy+(x-y)^2]/2
=[(x-y)^2+4xy+(x-y)^2]/2
=[36+84+36]/2
=36+42
=78
3（a+5)²+2(3—a)²+(9—a)(9+a)=0
3a^2+30a+75+2a^2-12a+18+81-a^2=0
4a^2+18a+174=0
2a^2+9a+87=0
△=9^2-4*2*87