bài 1 phân tích đa thức thành nhân tử e, $\frac{1}{4}$x ² – 5xy + 25y ² f, 36 – 12x + x ² g, (7x – 4) ² – (2x + 1) ² i, 49(x – 4) ² – 9(x + 2) ² gi

Đáp án:

$e, \frac{1}{4}x² – 5xy + 25y² $

$= (\frac{1}{2}x)² – 2.\frac{1}{2}.5xy + (5y)² $

$= (\frac{1}{2}x – 5y)² $

$f, 36 – 12x + x² $

$= 6² – 2.6x + x² $

$= (6 – x)²$

$g, (7x – 4)² – (2x + 1)² $

$= (7x – 4 – 2x – 1)(7x – 4 + 2x + 1) $

$= (5x – 5)(9x – 3) $

$=15(x – 1)(3x – 1) $

$i, 49(x – 4)² – 9(x + 2)² $

$= [7(x – 4)]² – [3(x + 2)]² $

$= (7x – 28)² – (3x + 6)² $

$= (7x – 28 – 3x – 6)(7x – 28 + 3x + 6) $

$= (4x – 34)(10x – 22) $

$= 4(2x – 17)(5x – 11)$