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The value of sin⁡75o−sin⁡15ocos⁡75o+cos⁡15o\frac{\sin75^o - \sin15^o}{\cos75^o + \cos15^o}cos75o+cos15osin75o−sin15o​ is​
Question

The value of sin75osin15ocos75o+cos15o\frac{\sin75^o - \sin15^o}{\cos75^o + \cos15^o} is​

A.

23\frac{2}{\sqrt3}​​

B.

3\sqrt3​​

C.

13\frac{1}{\sqrt3}​​

D.

None of these

Correct option is C

Given:

sin75sin15cos75+cos15\frac{\sin 75^\circ - \sin 15^\circ}{\cos 75^\circ + \cos 15^\circ}​​

Formula Used: 

sinAsinB=2cos(A+B2)sin(AB2)\sin A - \sin B = 2 \cos\left(\frac{A + B}{2}\right) \sin\left(\frac{A - B}{2}\right)​​

cosA+cosB=2cos(A+B2)cos(AB2)\cos A + \cos B = 2 \cos\left(\frac{A + B}{2}\right) \cos\left(\frac{A - B}{2}\right) 

Solution:

sin75sin15cos75+cos15 =2cos(75+152)sin(75152)2cos(75+152)cos(75152)\frac{\sin 75^\circ - \sin 15^\circ}{\cos 75^\circ + \cos 15^\circ}\\ \ \\= \frac{2 \cos\left(\frac{75^\circ + 15^\circ}{2}\right) \sin\left(\frac{75^\circ - 15^\circ}{2}\right)}{2 \cos\left(\frac{75^\circ + 15^\circ}{2}\right) \cos\left(\frac{75^\circ - 15^\circ}{2}\right)}​​

=2cos45sin302cos45cos30=\frac{2 \cos 45^\circ \sin 30^\circ}{2 \cos 45^\circ \cos 30^\circ}​​

sin30cos30 =tan30 =13 \frac{\sin 30^\circ}{\cos 30^\circ}\\ \ \\= \tan 30^\circ\\ \ \\ = \frac{1}{\sqrt{3}}​​

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