Question

tìm x
a) ( x - 1)^3 + 3(x+1)^2 = (x^2 - 2x + 4 )( x+ 2)
b) ( 2x -1 )(x+3) - x(3+2x) = 26

Answer 1

a) (x - 1)³ + 3(x + 1)² = (x² - 2x + 4)(x + 2)

x³ - 3x² + 3x - 1 + 3(x² + 2x+ 1) = x³ + 8

\(\Rightarrow\)x³ - 3x² + 3x - 1 + 3x² + 6x - x³ - 8 = 0

\(\Rightarrow\) 9x - 9 = 0

\(\Rightarrow\) 9x = 9

\(\Rightarrow\) x = 1

b) (2x - 1)(x + 3) - x(3 + 2x) = 26

2x² + 6x - x - 3 - 3x - 2x² = 26

2x - 3 = 26

\(\Rightarrow\) 2x = 29

\(\Rightarrow\) x = 14.5

Answer 2

a) ( x - 1)³ + 3(x+1)² = (x² - 2x + 4 )( x+ 2)

=>x³-3x²+3x-1+3(x²+2x+1)=x3+8

=>x³-3x²+3x-1+3x²+6x+3-x³-8=0

=>(x³-x³)+(-3x²+3x²)+(3x+6x)+(-1+3-8)=0

=>9x-6=0

=>9x=6

=>x=\(\dfrac{2}{3}\)

Answer 3

b) (2x-1)(x+3)-x(3+2x)=26

=>2x²+6x-x-3-3x-2x²=26

=>(2x²-2x²)+(6x-x-3x)-3=26

=>2x-3=26

=>2x=29

=>x=\(\dfrac{29}{2}\)

vậy x=\(\dfrac{29}{2}\)