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in Trigonometry by (29.9k points)
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Prove that

2cos215° - 1 = √3/2

1 Answer

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Best answer

To Prove: 2cos215° - 1 = √3/2

Taking LHS,

= 2 cos2 15° - 1 …(i)

We know that,

1 + cos 2x = 2 cos2x

Here, x = 15°

So, eq. (i) become

= [1 + cos 2(15°)] – 1

= 1 + cos 30° - 1

\(\frac{\sqrt{3}}{2}\)

= RHS

∴ LHS = RHS

Hence Proved

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