Question

Find the value of i) sin 19π/3 ii) cos 1140°iii) cot 25π/3​

Answer 1

5×sin15=21 , proved.

Step-by-step explanation:

To prove that, 2\sin 75 \times \sin 15=\dfrac{1}{2}2sin75×sin15=21 .

L.H.S. = 2\sin 75 \times \sin 152sin75×sin15

=2\sin 75 \times \sin (90-75)=2sin75×sin(90−75)

Using the trigonometric identity,

\cos A=\sin (90-A)cosA=sin(90−A)

=2\sin 75 \times \cos 75=2sin75×cos75

Using the trigonometric identity,

\sin 2A=2\sin A \times \cos Asin2A=2sinA×