9x + 9x-1 = 90 then x = ……………….. A) 2 B) -2C) 3 D) 4

1.	9x + 9x-1 = 90 then x = ……………….. A) 2 B) -2C) 3 D) 4
Answer» 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 Correct option is A) 2 9^2 + 9^2-1 (9)^2 +(9)^1 81+9 90 the correct option is A

Answer»

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

Correct option is A) 2

the correct option is A

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