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Question

Mathematics Question on Differentiability

The derivative of sinxcosx\sin x^{\circ} \, \, \cos x with respect to xx is

A

π180(cosxcosxsinxsinx)\frac{\pi}{180} (\cos \, x^{\circ} \, \cos \, x - \sin \, x^{\circ} \sin \, x)

B

π180cosxcosxsinxsinx\frac{\pi}{180} \cos \, x^{\circ} \, \cos \, x - \sin \, x^{\circ} \sin \, x

C

180π(cosxcosxsinxsinx)\frac{180}{\pi} (\cos \, x^{\circ} \, \cos \, x - \sin \, x^{\circ} \sin \, x)

D

π180cosxsinx- \frac{\pi}{180} \cos \, x^{\circ} \, \sin \, x

Answer

π180cosxcosxsinxsinx\frac{\pi}{180} \cos \, x^{\circ} \, \cos \, x - \sin \, x^{\circ} \sin \, x

Explanation

Solution

It is given that sinxcosx\sin x^{\circ}\, \cos x .
First we change xx^{\circ} into radian
i.e.,i.e., 1 degree =π180= \frac{\pi}{180} radian
x=π180x\Rightarrow \, \, \, x^{\circ} = \frac{\pi}{180} x redian
sinx.cosx=sin(π180x)cosx\therefore \, \, \, \, \sin x^{\circ} . \cos x = \sin \left(\frac{\pi}{180} x \right) \cos x
Now differentiating w.r.t. x'x', we have
[cos(π180x).(π180)cosx]+sin(π180x)(sinx)\Rightarrow \left[\cos\left(\frac{\pi}{180} x\right).\left(\frac{\pi}{180}\right) \cos x\right] +\sin\left(\frac{\pi}{180}x\right)\left(-\sin x\right)
π180cosxcosxsinxsinx\Rightarrow \frac{\pi}{180} \cos x^{\circ} \cos x -\sin x^{\circ} \sin x