Question

Tìm x

a) (2x-3)²=(4-5x)²

b)9x²-16=3x-4

c)5.(x-1)³=20.(x-1) 

Answer 1

(2x-3)²=(4-5x)²

 => 2x-3=4-5x

 =>     7x=7

 =>       x =1

Answer 2

(2x-3)²=(4-5x)²

 => 2x-3=4-5x

 =>     7x=7

 =>       x =1

Answer 3

a)

\(\left(2x-3\right)^2=\left(4-5x\right)^2\)

\(\hept{\begin{cases}2x-3=4-5x\\2x-3=-4+5x\end{cases}\Leftrightarrow}\hept{\begin{cases}7x=7\\-3x=-1\\x=1,\frac{1}{3}\end{cases}}\)

b)

\(9x^2-3x-12=0\)

denta =  \(9-4.9.-12=21^2\)

\(\hept{\begin{cases}x1=\frac{3-21}{18}=1\\x2=\frac{3+21}{18}=\frac{24}{18}=\frac{4}{3}\end{cases}}\)

c)  \(5\left(x-1\right)^3-20\left(x-1\right)=\left(x-1\right)\left(5\left(x-1\right)^2-20\right)=0\)

x1=1

\(x2=\left(5\left(x^2-2x+1\right)-20\right)=0\)

\(x2=5x^2-2x-19=0\)

\(\Delta=4-4.-19.5=384\)

\(x3=\frac{2-\sqrt{384}}{10}\)

\(x4=\frac{2+\sqrt{384}}{10}\)