prove

Question

cos squared B- sin squared B= 2cos squared B -1

Answer 1

cos^2 B - sin^2 B = 2cos^ B - 1

LS
= cos^2 B - (1 - cos^2 B)
= 2cos^2 B - 1
= RS

Answer 2

substitute 1 - cos^2B for sin^2 B