Question

I. Tìm x

a. \(\left|x\right|=1,21\)

b. \(\dfrac{11}{12}-\left(\dfrac{2}{5}-x\right)=\dfrac{2}{3}\)

c. \(\dfrac{3}{4}+\dfrac{1}{4}\div x=\dfrac{2}{5}\)

d. \(3^x=81\)

e. \(\dfrac{1}{2}\times\left|x\right|-\dfrac{5}{2}=\dfrac{8}{3}\)

f. \(2^{x-3}=4\)

Answer 1

I , tìm x :

a, \(\left|x\right|=1,21\)

Ta có : \(\left|x\right|=\left|1,21\right|\rightarrow\left|x\right|=\pm1,21\)

b, \(\dfrac{11}{12}-\left(\dfrac{2}{5}-x\right)=\dfrac{2}{3}\)

\(\dfrac{2}{5}-x=\dfrac{11}{12}-\dfrac{2}{3}\)

\(\dfrac{2}{5}-x=\dfrac{1}{4}\) => \(x=\dfrac{2}{5}-\dfrac{1}{4}\)

=> \(x=\dfrac{3}{20}\)

c, \(\dfrac{3}{4}+\dfrac{1}{4}:x=\dfrac{2}{5}\)

\(\dfrac{1}{4}\div x=\dfrac{2}{5}-\dfrac{3}{4}\)

\(\dfrac{1}{4}\div x=\dfrac{-7}{20}\) => \(x=\dfrac{1}{4}\div\dfrac{-7}{20}\)

=> \(x=\dfrac{-5}{7}\)

d,\(3^x=81\)

Ta có 81= \(3^4\)

Vì : \(3^x=3^4\Rightarrow x=4\)

e,\(\dfrac{1}{2}.\left|x\right|-\dfrac{5}{2}=\dfrac{8}{3}\)

\(\left|x\right|-\dfrac{5}{6}=\dfrac{8}{3}:\dfrac{1}{2}\)

=> \(\left|x\right|-\dfrac{5}{2}=\dfrac{16}{3}\) => \(\left|x\right|=\dfrac{16}{3}+\dfrac{5}{2}\)

=> \(\left|x\right|=\dfrac{47}{6}\)

Vì \(\left|x\right|=\left|\dfrac{47}{6}\right|\Rightarrow x=\pm\dfrac{47}{6}\)

f, \(2^{x-3}=4\)

\(2^{x-3}=2^2\)

=> \(x-3=2\)

=> \(x=5\)

Answer 2

a, Ta có \(\left|x\right|=1,21\)

\(\Rightarrow\left[{}\begin{matrix}x=1,21\\x=-1,21\end{matrix}\right.\)

Vậy \(x\in\left\{1,21;-1,21\right\}\)