Question

$\left\{ \cos^{–1}\left( \frac{4x^{3}}{27}–x \right) \right\}$ is :

• A. $\frac{3}{\sqrt{9–x^{2}}}$
• B. $\frac{1}{\sqrt{9–x^{2}}}$
• C. $\frac{–3}{\sqrt{9–x^{2}}}$
• D. $\frac{–1}{\sqrt{9–x^{2}}}$

Answer 1

Answer: (C)

$\frac{–3}{\sqrt{9–x^{2}}}$

Answer 2

$\frac{d}{dx}$ [cos^–1(4.(x/3)³ –3(x/3))]

=$\frac{d}{dx}$ [3cos^–1(x/3)]

= 3. $\frac{1}{3}$= $\frac{–3}{\sqrt{9–x^{2}}}$