(1)(-2a)3-(-a)(3a)2 =-8a3-(-a)(9a2) =-8a3+9a3 =a3;
(2)(a+3)(a2-9)(a-3) =(a2-9)(a2-9) =a4-18a2+81;
(3)(-3)0+(-)-2÷|-2| =1+4÷2 =1+2 =3;
(4)(x+3)2-(x-1)(x-2) =x2+6x+9-(x2-3x+2) =x2+6x+9-x2+3x-2 =9x+7;
(5), 由②得,y=2x-8③, ③代入①得,3x+2(2x-8)=5, 解得x=3, 把x=3代入③得,y=6-8=-2, 所以,方程组的解是;
(6), ①+②得,4x+8=0, 解得x=-2, 把x=-2代入①得,-6-y+2=0, 解得y=-4, 所以,方程组的解是. |