Prove the following \(\displaystyle{{\sin}^{{4}}{x}}+{{\cos}^{{{15}}}{x}}={1}\)

xxgetthisar08

xxgetthisar08

Answered question

2022-03-31

Prove the following
sin4x+cos15x=1

Answer & Explanation

Pubephenedsjq

Pubephenedsjq

Beginner2022-04-01Added 11 answers

As 0cos2x1, cos15xcos4x=cos4x(cos11x1)0
sin4x+cos4xsin4x+cos4x
Now, sin4x+cos4x=(sin2x+cos2x)22sin2xcos2x=12sin2xcos2x1
The equality occurs if one of sinx,cosx is 0
If cosx=0, sinx=±1sin4x=1
If sinx=0, cosx=±1cos15x=±1
So, we can clearly identify when the given proposition holds.

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