Question

sec^4-cos^4=1-2cos^2 give proof...​

Answer 1

The question is wrong...in place of sec^4 its sin^4...

now,

sin^4 -cos^4

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

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

=(1)(1-cos^2-cos^2)

=1-2cos^2

Here is the answer...