Question

Prove that :- sin4 – cos4 = 1-2 cos2 .
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Answer 1

Answer:

Given:

cos

4

A−sin

4

A+1=(cos

2

A−sin

2

A)(cos

2

A+sin

2

A)+1

=cos

2

A−sin

2

A+1

=cos

2

A+cos

2

A

=2cos

2

A