Home Opt. Mathematics Prove that: cos^2(A+120)+cos^2(A-120)+cos^2(A) = 3/2

Thursday, February 1, 2018

Prove that: cos^2(A+120)+cos^2(A-120)+cos^2(A) = 3/2


Soln:
Use formula:
cos2A = 2cos^2(A) - 1
cos2A+1= 2cos^2(A)
(1+cos2A)/2 = cos^2(A)
i.e. cos^2(A)  = (1+cos2A)/2