| (1)原式=(-x) 2 -(3y) 2 =x 2 -9y 2 ; (2)原式=4a 4 b 2 ?6ab÷(-3b 2 ) =24a 5 b 3 ÷(-3b 2 ) =-8a 5 b 3 ; (3)原式=6x 2 +4x-3x-2-(6x 2 -12x) =6x 2 +4x-3x-2-6x 2 +12x =13x-2; (4)原式=2a 2 -4a+1; (5)原式=9x 2 -6xy+y 2 -(9x 2 -4y 2 ) =9x 2 -6xy+y 2 -9x 2 +4y 2 =5y 2 -6xy. |