Question

81 mũ  -2x nhân 27 mũ x = 9 mũ 5

Answer 1

khó vãi

Answer 2

ai jup tui với

Answer 3

81^-2x.27^x = 9⁵

81^-2x(3³)^x = 9⁵

3^4(-2x).(3³)^x = 9⁵

3^4(-2x).3^3x = 9⁵

3^{4(-2x) + 3x} = 9⁵

3^{4(-2x) + 3x} = (3²)⁵

3^{4(-2x) + 3x} = 3^2.5

4(-2x) + 3x = 2.5

-5x = 10

x = -2

Answer 4

Cách làm khác : 

\(81^{-2x}\cdot27^x=9^5\)

\(\frac{1}{81^{2x}}\cdot27^x=9^5\)

\(\frac{27^x}{81^{2x}}=9^5\)

\(\frac{\left(3^3\right)^x}{\left(3^4\right)^{2x}}=\left(3^2\right)^5\)

\(\frac{3^{3x}}{3^{8x}}=3^{10}\)

\(\frac{1}{3^{5x}}=3^{10}\)

\(3^{10}\cdot3^{5x}=1\)

\(3^{10+5x}=3^0\)

\(\Rightarrow\text{ }10+5x=0\)

\(5x=0-10=-10\)

\(x=-10\text{ : }5\)

\(x=-2\)