Câu hỏi của Thuy Tran

Question

Tìm x:

a) 27x .9x = 927:81

b)$\left(\dfrac{12}{25}\right)^x=\left(\dfrac{5}{3}\right)^{-2}-\left(\dfrac{-3}{5}\right)^4$

Nguyễn Thanh Hằng · Accepted Answer

a/ $27^x.9^x=9^{27}:81$

$\Leftrightarrow3^{3x}.3^{2x}=3^{54}:3^4$

$\Leftrightarrow3^{2x+3x}=3^{50}$

$\Leftrightarrow2x+3x=50$

$\Leftrightarrow5x=50$

$\Leftrightarrow x=10$

Vậy ...Câu trả lời: a/ $27^x.9^x=9^{27}:81$

$\Leftrightarrow3^{3x}.3^{2x}=3^{54}:3^4$

$\Leftrightarrow3^{2x+3x}=3^{50}$

$\Leftrightarrow2x+3x=50$

$\Leftrightarrow5x=50$

$\Leftrightarrow x=10$

Vậy ...

ChaosKiz · Answer

$a.27^x.9^x=9^{27}:81$

$\left(3^3\right)^x.\left(3^2\right)^x=\left(3^2\right)^{27}:\left(3^2\right)^2$

$3^{3x}.3^{2x}=3^{50}$

$3^{3x+2x}=3^{50}$

$\Rightarrow3x+2x=50$

$x\left(3+2\right)=50$

$x=50:5=10$

Vậy$x=10$

$b.\left(\dfrac{12}{25}\right)^x=\left(\dfrac{5}{3}\right)^{-2}-\left(-\dfrac{3}{5}\right)^4$

$\left(\dfrac{12}{25}\right)^x=\dfrac{9}{25}-\dfrac{81}{625}$

$\left(\dfrac{12}{25}\right)^x=\dfrac{144}{625}$( Đề sai )Câu trả lời: $a.27^x.9^x=9^{27}:81$