Question

[Cậu Nhok Thám Tử]

Tìm x biết:

\(7^{2+x}+2\times7^{x-1}=345\)

\(81^{-2\times x}\times27^x=9^5\)

\(\left(\dfrac{1}{3}-\dfrac{1}{2}\right)^{x-1}=\dfrac{1}{36}\)

\(\dfrac{25}{5^x}=\dfrac{1}{125}\)

\(\dfrac{\left(-7\right)^{2\times x-1}}{49}=-343\)

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(\Leftrightarrow7^x\cdot49+7^x\cdot\dfrac{2}{7}=345\)

\(\Leftrightarrow7^x=7\)

hay x=1

c: \(\left(\dfrac{1}{3}-\dfrac{1}{2}\right)^{x-1}=\dfrac{1}{36}\)

\(\Leftrightarrow\left(-\dfrac{1}{6}\right)^{x-1}=\left(-\dfrac{1}{6}\right)^2\)

=>x-1=2

hay x=3

d: \(\dfrac{25}{5^x}=\dfrac{1}{125}\)

\(\Leftrightarrow5^x=5^2\cdot5^3=5^5\)

hay x=5