Câu hỏi của Vũ Gia Linh

Question

Tìm x:

a) [(x-81)³:5³]-2³=0

b)3ⁿ⁺¹.3ⁿ⁺³=18¹⁰:6¹⁰

Dang Tung · Accepted Answer

a)

$\left[\left(x-81\right)^3:5^3\right]-2^3=0\ =>\left(x-81\right)^3:5^3=2^3\ =>\left(x-81\right)^3=2^3.5^3=10^3\ =>x-81=10\ =>x=91$

b)

$3^{n+1}.3^{n+3}=18^{10}:6^{10}\ =>3^{n+1+n+3}=3^{10}\ =>2n+4=10\ =>2n=6=>n=3$

Câu trả lời:

a)

$\left[\left(x-81\right)^3:5^3\right]-2^3=0\ =>\left(x-81\right)^3:5^3=2^3\ =>\left(x-81\right)^3=2^3.5^3=10^3\ =>x-81=10\ =>x=91$

b)

$3^{n+1}.3^{n+3}=18^{10}:6^{10}\ =>3^{n+1+n+3}=3^{10}\ =>2n+4=10\ =>2n=6=>n=3$

HT.Phong (9A5) · Answer

a) $\left[\left(x+81\right)^3:5^3\right]-2^3=0$

$\Rightarrow\left(\dfrac{x+81}{5}\right)^3=2^3$

$\Rightarrow\dfrac{x-81}{5}=2$

$\Rightarrow x-81=10$

$\Rightarrow x=91$

b) $3^{n+1}\cdot3^{n+3}=18^{10}:6^{10}$

$\Rightarrow3^{2n+4}=3^{10}$

$\Rightarrow2n+4=10$

$\Rightarrow2n=6$

$\Rightarrow n=3$