Question

[phamhoangthienanh]

- Giúp mk vs 

Tìm x : 

a , x/x + 3 = 2/5 

b, ( x + 1/2 )² - 1/3 = 1/9

c, ( x - 1/2 )³ + 1/4 = 3/8 

d, 2^x+3 = 32

e, 3^x+2 + 3^x = 90 

Answer 1

[Đức Phạm]

b, \(\left(x+\frac{1}{2}\right)^2-\frac{1}{3}=\frac{1}{9}\)

\(\Leftrightarrow\left(x+\frac{1}{2}\right)^2=\frac{4}{9}\)

\(\Leftrightarrow\left(x+\frac{1}{2}\right)^2=\left(\frac{2}{3}\right)^3\)

\(\Leftrightarrow x+\frac{1}{2}=\frac{2}{3}\Rightarrow x=\frac{1}{6}\)

c, \(\left(x-\frac{1}{2}\right)^3+\frac{1}{4}=\frac{3}{8}\)

\(\Leftrightarrow\left(x-\frac{1}{2}\right)^3=\frac{1}{8}\)

\(\Leftrightarrow\left(x-\frac{1}{2}\right)^3=\left(\frac{1}{2}\right)^3\)

\(\Leftrightarrow\orbr{\begin{cases}x-\frac{1}{2}=\frac{1}{2}\\x-\frac{1}{2}=-\frac{1}{2}\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x=1\\x=0\end{cases}}\)

Answer 2

[Đức Phạm]

d, \(2^{x+3}=32\)

\(\Leftrightarrow2^{x+3}=2^5\Leftrightarrow x+3=5\Rightarrow x=2\)

e, \(3^{x+2}+3^x=90\)

\(\Rightarrow\)\(3^x.\left(3^2+1\right)=90\)

\(\Rightarrow\)\(3^x.10=90\Rightarrow3^x=9\Rightarrow3^x=3^2\Rightarrow x=2\)