Question

a.3.(X+1/2)=7/4-2/3

b.(2x-5)^2=81

c.(3x-4)^3=27

tìm x

 

 

Answer 1

\(3\cdot\left(x+\dfrac{1}{2}\right)=\dfrac{7}{4}-\dfrac{2}{3}\)

\(3\cdot\left(x+\dfrac{1}{2}\right)=\dfrac{21}{12}-\dfrac{8}{12}\)

\(3\cdot\left(x+\dfrac{1}{2}\right)=\dfrac{13}{12}\)

\(x+\dfrac{1}{2}=\dfrac{13}{12}\cdot\dfrac{1}{3}\)

\(x+\dfrac{1}{2}=\dfrac{13}{36}\)

\(x=\dfrac{13}{36}-\dfrac{1}{2}=\dfrac{13}{36}-\dfrac{18}{36}\)

\(x=-\dfrac{5}{36}\)

\(\left(2x-5\right)^2=81\)

\(4x^2-20x+25=81\)

\(4x^2-20x-56=0\)

\(4\cdot\left(x+2\right)\left(x-7\right)=0\)

\(\left[{}\begin{matrix}x+2=0\\x-7=0\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x=-2\\x=7\end{matrix}\right.\Rightarrow x\in\left\{-2;7\right\}\)

\(\left(3x-4\right)^3=27\)

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

`=>3x-4=3`

`3x=7`

`=>x=7/3`