ABC26GN2066 · Logarithms

Subject: General Aptitude · Chapter: Logarithms · Exam: 2007 · Marks: · Difficulty:

If $\log _{5}\left(x^{2}+x\right)-\log _{5}(x+1)=2$, then the value of $x$ is
(a)5
(b)10
(c)25
(d)32
Answer
Answer (as printed): C
Explanation
$\log _{5}\left(x^{2}+x\right)-\log _{5}(x+1)=2$ $$\begin{aligned} & \Rightarrow \log _{5}\left(\frac{x^{2}+x}{x+1}\right)=2 \Rightarrow \log _{5}\left[\frac{x(x+1)}{x+1}\right]=2 \\ & \Rightarrow \log _{5} x=2 \Rightarrow x=5^{2}=25 \end{aligned}$$

Explanation as extracted from the printed page; notation may be imperfect.

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