Question

Tìm x:

a) (x-1)³-(-\(\frac{3}{4}\))=\(\frac{7}{8}\)

b)3^x-1=\(\frac{1}{243}\)

Answer 1

a, \(\left(x-1\right)^3-\left(-\frac{3}{4}\right)=\frac{7}{8}\)

\(\left(x-1\right)^3=\frac{7}{8}+\left(-\frac{3}{4}\right)\)

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

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

\(x-1=\frac{1}{2}\)

\(x=\frac{1}{2}+1\)

\(x=\frac{3}{2}\)

Answer 2

b, \(3^{x-1}=\frac{1}{243}\)

Ta có : \(3^{-5}=\frac{1}{243}\)

=> x - 1 = -5

=> x = -4

Answer 3

a) \(\left(x-1\right)^3-\left(-\frac{3}{4}\right)=\frac{7}{8}\)

⇒ \(\left(x-1\right)^3=\frac{7}{8}+\left(-\frac{3}{4}\right)\)

⇒ \(\left(x-1\right)^3=\frac{1}{8}\)

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

⇒ \(x-1=\frac{1}{2}\)

⇒ \(x=\frac{1}{2}+1\)

⇒ \(x=\frac{3}{2}\)

Vậy \(x=\frac{3}{2}.\)

b) \(3^{x-1}=\frac{1}{243}\)

⇒ \(3^{x-1}=3^{-5}\)

⇒ \(x-1=-5\)

⇒ \(x=\left(-5\right)+1\)

⇒ \(x=-4\)

Vậy \(x=-4.\)

Chúc bạn học tốt!