(1)原式=(a-b)(x-y)+(a-b)(x+y)=(a-b)(x-y+x+y)=2x(a-b)(2)原式=2²+2×3×(x-y)+[3(x-y)]²=(2+3x-3y)²=(3x-3y+2)²
2(a-b)x (3x-3y+2)^2