Вправи: 820

820. Скоротіть дріб:

1) 3x-6y3x = 3(x-2y)3x = x-2yx;

2) 3a+9b4a+12b = 3(a+3b)4(a+3b) = 34;

3) a2-493a+21 = (a-7)(a+7)3(a+7) = a-73;

4) 12x2-4x2-6x = -4x(3x-1)2(3x-1) = –2x;

5) x2-9x2+6x+9 = (x-3)(x+3)(x+3)2 = x-3x+3;

6) b7+b4b2+ b5 = b4(b2+1)b2(b3+1) = b².