MCQ
$\lim _{x \rightarrow 0} \frac{\sin 7 x \cdot \sin 11 x}{5 x^2}=$
  • A
    $\frac{89}{5}$
  • B
    $\frac{56}{3}$
  • $\frac{77}{5}$
  • D
    $\frac{65}{3}$

Answer

Correct option: C.
$\frac{77}{5}$
(C)
$\lim _{x \rightarrow 0} \frac{\sin 7 x \cdot \sin 11 x}{5 x^2}$
$=\frac{1}{5} \lim _{x \rightarrow 0} \frac{\sin 7 x}{x} \times \lim _{x \rightarrow 0} \frac{\sin 11 x}{x}$
$=\frac{1}{5} \lim _{x \rightarrow 0} \frac{\sin 7 x}{7 x} \times 7 \times \lim _{x \rightarrow 0} \frac{\sin 11 x}{11 x} \times 11$
$=\frac{1}{5} \times 7 \times 11$
$=\frac{77}{5}$

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