Question

(Cos⁴x - sin⁴x) is equal to
(a) 2sin²x - 1 (b) 1 - 2cos²x (c) sin²x - cos²x (d)2cos²x - 1

Answer 1

Answer:

cos⁴x - sin ⁴x

=( cos²x)² - ( sin²x)²

= ( sin²x + cos²x)( sin²x - cos²x)

= 1*(sin²x - cos²x)

= (1- cos²x - cos²x)

= 1 - 2cos²x

so the correct answer is option b

Answer 2

Answer:

b)   1-2cos^2x

Step-by-step explanation:

cos⁴x - sin ⁴x

=( cos²x)² - ( sin²x)²

= ( sin²x + cos²x)( sin²x - cos²x)

= 1*(sin²x - cos²x)

= (1- cos²x - cos²x)

= 1 - 2cos²x