Question

9^x + 9^x-1 = 90 then x = ……………….. 

A) 2 

B) -2

C) 3 

D) 4

Answer 1

Correct option is (A) 2

\(9^x+9^{x-1}\) = 90

\(\Rightarrow\) \(9^{x-1}(9+1)=90\)

\(\Rightarrow\) \(9^{x-1}\times10=90\)

\(\Rightarrow\) \(9^{x-1}=\frac{90}{10}=9\)

\(\Rightarrow\) x - 1 = 1

\(\Rightarrow\) x = 1 - (-1) = 1+1 = 2

Answer 2

Correct option is  A) 2

Answer 3

• 9^2 + 9^2-1
• (9)^2 +(9)^1
• 81+9
• 90

the correct option is A