BT1:
a) (3x - 4) (3x + 4) + (3x - 1)²
= (3x)² - 4² + 9x² - 6x + 1
= 9x² - 16 + 9x² - 6x + 1
= (9x² + 9x²) + (-16 + 1) - 6x
= 18x² - 15 - 6x
b) (2x + 5)² - 4x(x - 3)
= 4x² + 20x + 25 - 4x² + 12x
= (4x² - 4x²) + (20x + 12x) + 25
= 32x + 25
c) (x - 6)² - (x + 2) (x + 7)
= x² - 12x + 36 - (x² + 7x + 2x + 14)
= x² - 12x + 36 - (x² + 9x + 14)
= x² - 12x + 36 - x² - 9x - 14
= (x² - x²) + (-12x - 9x) + (36 - 14)
= -21x + 22
d) 6x(x + 1) - (4x - 5) (4x + 5)
= 6x² + 6x - (16x² - 15)
= 6x² + 6x - 16x² + 15
= (6x² - 16x²) + 6x + 15
= -10x²+ 6x + 15
BT2:
(2x - 3)² + (x + 2) (3 - 4x) = 66
4x² - 12x + 9 + 3x - 4x² + 6 - 8x = 66
(4x² - 4x²) + (-12x + 3x - 8x) + (9 + 6) = 66
-17x + 15 = 66
-17x = 66 - 15
-17x = 51
x = $\frac{-51}{17}$
Chúc bn học tốt!!!
vote 5*, ctlhn nha bn
