Question

c.\(\dfrac{5^{11}}{7^{11}}.x=\left(\dfrac{5}{7}\right)^{12}.7\)

d.\(9^{x+2}+9^x-9^2.82=0\left(x\in N\right)\)

Answer 1

c: \(\Leftrightarrow x\cdot\left(\dfrac{5}{7}\right)^{11}=\left(\dfrac{5}{7}\right)^{12}\cdot7\)

\(\Leftrightarrow x=\left(\dfrac{5}{7}\right)^{12}:\left(\dfrac{5}{7}\right)^{11}\cdot7=\dfrac{5}{7}\cdot7=5\)

d: \(\Leftrightarrow9^x\cdot81+9^x-9^2\cdot82=0\)

\(\Leftrightarrow9^x\cdot82=9^2\cdot82\)

\(\Leftrightarrow9^x=9^2\)

hay x=2

Answer 2

c: ⇔x=(5/7)mũ12:(57)mũ11⋅7=5/7⋅7=5

d: 

vậy x=2