Question

The value of cos^4 A-sin^4 A is
(a) sin 2A
(b)cos 2A
(c) tan 2A
(d) sec 2A​

Answer 1

Answer:

(b) cos2A is the answer

Step-by-step explanation:

cos ^4A-sin^4A

=(cos^2A)^2-(sin^2A)^2. {a^2-b^2=(a+b)(a-b)}

=(cos^2A+sin^2A)(cos^2A-sin^2A)

=1(cos2A)

=cos2A