Question

Prove that: sin^4 θ - cos^4 θ = 1 - 2 cos^2 θ

PLZZZ ANSWER​

Answer 1

Answer:

sin⁴a - cos⁴a= 1-2cos²a

=(sin²a+cos²a)(sin²a-cos²a)

=1(sin²a-cos²a)

=(sin²a-cos²a)

using;

sin²a=1-cos²a

it becomes;

=1-cos²a-cos²a

=1-2cos²a=R.H.S