Question

bài tập 42 sgk lớp 7 tập 1 trang 23

Answer 1

a) \(\dfrac{16}{2^n}=2\Rightarrow2^n=\dfrac{16}{2}\Rightarrow2^n=8\)

Ta có: \(2^3=8\Rightarrow n=3\)

b) \(\dfrac{\left(-3\right)^n}{81}=-27\Rightarrow\left(-3\right)^n=\left(-27\right).81\)

\(\Rightarrow\left(-3\right)^n=-2187\)

Ta có: - 2187 = ( -3 ) ⁷

\(\Rightarrow n=7\)

c) \(8^n:2^n=4=\left(\dfrac{8}{2}\right)^n=4\Rightarrow4^n=4\)

\(\Rightarrow n=1\)