Câu hỏi của Nguyễn Thị Thanh Nhàn

Question

bài tập 42 sgk lớp 7 tập 1 trang 23

Phạm Tú Uyên · Accepted Answer

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

$\Rightarrow n=1$Câu trả lời: 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) $8^n:2^n=4=\left(\dfrac{8}{2}\right)^n=4\Rightarrow4^n=4$

$\Rightarrow n=1$