MCQ
$\lim _{x \rightarrow 9}\left(\frac{x^{3 / 2}-27}{x-9}\right)=$
  • A
    $\frac{3}{2}$
  • $\frac{9}{2}$
  • C
    $\frac{2}{3}$
  • D
    $\frac{1}{3}$

Answer

Correct option: B.
$\frac{9}{2}$
(B)
$\lim _{x \rightarrow 9}\left(\frac{x^{3 / 2}-27}{x-9}\right)$
$=\lim _{x \rightarrow 9}\left(\frac{(\sqrt{x})^3-3^3}{(\sqrt{x}+3)(\sqrt{x}-3)}\right)$
$=\lim _{x \rightarrow 9}\left(\frac{(\sqrt{x}-3)(x+3 \sqrt{x}+9)}{(\sqrt{x}+3)(\sqrt{x}-3)}\right)$
$=\frac{9+3 \sqrt{9}+9}{\sqrt{9}+3}$
$=\frac{27}{6}$
$=\frac{9}{2}$

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