What is the value of 2cos2 15° – 1 ?
1. \(\frac 12\)
2. \(\frac 1 {\sqrt 2}\)
3. \(\frac {\sqrt 3}2\)
4. \(\sqrt 3 – 1\)
1. \(\frac 12\)
2. \(\frac 1 {\sqrt 2}\)
3. \(\frac {\sqrt 3}2\)
4. \(\sqrt 3 – 1\)
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Correct Answer – Option 3 : \(\frac {\sqrt 3}2\)
Concept:
2cos2 θ – 1 = cos 2θ
Calculations:
Consider, 2cos2 15° – 1
= cos 2 (15°)
= cos (30°)
= \(\dfrac {\sqrt 3}2\)