MCQ
$\lim _{x \rightarrow 0} \frac{a^{3 x}-a^{2 x}-a^x+1}{x^2}$ is equal to
  • A
    $\sqrt{2} \log a^2$
  • B
    $\sqrt{2} \log a$
  • $2(\log a)^2$
  • D
    $2(\log a)^3$

Answer

Correct option: C.
$2(\log a)^2$
(C)
$\lim _{x \rightarrow 0} \frac{ a ^{3 x}- a ^{2 x}- a ^x+1}{x^2}$
$=\lim _{x \rightarrow 0} \frac{ a ^{2 x} \cdot a ^x- a ^{2 x}- a ^x+1}{x^2}$
$=\lim _{x \rightarrow 0} \frac{\left( a ^{2 x}-1\right)\left( a ^x-1\right)}{x^2}$
$=2 \log a \cdot \log a =2(\log a )^2$

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