Question

If cos⁴a-sin⁴a= 2/3
then find the value of 2cos²a-1?​

Answer 1

Answer:

hope this will help you

Answer 2

Answer:  2/3

Step-by-step explanation:

$cos^{4}a-sin^{4}a =(cos^2a-sin^2a ) \times(cos^2a+sin^2a)\\cos^{4}a-sin^{4}a=(cos^2a-sin^2a ) =cos2a =2cos^2a-1 \\ \\\\\\as (cos^2a+sin^2a)=1\\and (cos^2a-sin^2a) =cos2a=2cos^2a-1\\\\2cos^2a-1=2/3$