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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)
b) \(\frac{2}{5}\)x2 + 5x3 + x2y = x2 (\(\frac{2}{5}\) + 5x + y)
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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)