Bài 3:
a) Ta có: \(\dfrac{\left(-2\right)^x}{16}=-8\)
\(\Leftrightarrow\left(-2\right)^x=-128\)
\(\Leftrightarrow x=7\)
b) Ta có: \(\left(1-x\right)^3=-64\)
\(\Leftrightarrow1-x=-4\)
\(\Leftrightarrow x=5\)
c) Ta có: \(\dfrac{20^x}{5^x}=256\)
\(\Leftrightarrow4^x=256\)
\(\Leftrightarrow x=4\)
d) Ta có: \(25\le5^x\le5\cdot5^4\)
\(\Leftrightarrow2\le x\le5\)
\(\Leftrightarrow x\in\left\{2;3;4;5\right\}\)
e) Ta có: \(\left|x+0.5\right|-1=0\)
\(\Leftrightarrow\left|x+0.5\right|=1\)
\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{1}{2}=1\\x+\dfrac{1}{2}=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{2}\\x=\dfrac{-3}{2}\end{matrix}\right.\)
Bài 3:
f) Ta có: \(\dfrac{1}{9}\cdot3^4\cdot3^x=3^7\)
\(\Leftrightarrow3^{x+2}=3^7\)
\(\Leftrightarrow x+2=7\)
hay x=5
Bài 4:
a) Ta có: \(\left(-3\right)^4=81\)
\(\left(-3\right)^3=-27\)
mà 81>-27
nên \(\left(-3\right)^4>\left(-3\right)^3\)
giải giúp mình với