UPSC NDA Math Model Paper 9

Here, we have to find the value of sin 75° sin 15° + cos 75° cos 15°
As we know that, cos x cos y + sin x sin y = cos (x - y)
∴ sin 75° sin 15° + cos 75° cos 15° = cos 75° cos 15° + sin 75° sin 15°
= cos (75° - 15°)
= cos 60°
=

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