39. Phân tích các đa thức sau thành nhân tử:
a) 3x - 6y; b) \(\frac{2}{5}\)x2 + 5x3 + x2y;
c) 14x2y – 21xy2 + 28x2y2; d) \(\frac{2}{5}\)x(y - 1) - \(\frac{2}{5}\)y(y - 1);
e) 10x(x - y) - 8y(y - x).
a) 3x - 6y = 3 . x - 3 . 2y = 3(x - 2y)
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b) \(\frac{2}{5}\)x2 + 5x3 + x2y = x2 (\(\frac{2}{5}\) + 5x + y)
c) 14x2y – 21xy2 + 28x2y2 = 7xy . 2x - 7xy . 3y + 7xy . 4xy = 7xy(2x - 3y + 4xy)
d) \(\frac{2}{5}\)x(y - 1) - \(\frac{2}{5}\)y(y - 1) = \(\frac{2}{5}\)(y - 1)(x - y)
e) 10x(x - y) - 8y(y - x) =10x(x - y) - 8y[-(x - y)]
= 10x(x - y) + 8y(x - y)
= 2(x - y)(5x + 4y)