Question

tìm x biết

a, ( x + 5 )^{2 -} ( x - 3 )² = 2x - 7

b, ( 2x - 3 ) . ( 4x² + 6x + 9 ) = 98

c, ( \(\dfrac{1}{9}\)x2 + \(\dfrac{2}{3}\)x + 4 ) . ( \(\dfrac{1}{3}\)x - 2 ) = 56

d, 16x³ - 12x² + 3x - 7 = 0

Answer 1

a) (x + 5)² - (x - 3)² = 2x - 7

(x + 5 - x + 3)(x + 5 + x - 3) = 2x - 7

8(2x + 2)= 2x - 7

16x + 16 = 2x - 7

16x - 2x = - 7 - 16

14x = - 23

x = - 23/14

b) (2x - 3)(4x² + 6x + 9) = 98

(2x)³ - 3³ = 98

8x³ - 27 = 98

8x³ = 125

x³ = 125/8

x³ = (5/2)³

x = 5/2