Question

cos4a+sin4a=1-2cos2asin2a
​

Answer 1

Answer:

sin

4

A+cos

4

A

We have (a

2

+b

2

)

2

=a

4

+b

4

+2a

2

b

2

⇒a

4

+b

4

=(a

2

+b

2

)

2

−2a

2

b

2

Take a=sinA and b=cosA we get

sin

4

A+cos

4

A=(sin

2

A+cos

2

A)

2

−2sin

2

Acos

2

A

=1−2sin

2

Acos

2

A proved.