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

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

$\Rightarrow2n+4=10$

$\Rightarrow2n=6$

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