buktikan bahwa cos^2 alfa=1/2+1/2(cos^2-sin^2)

Trigonometri

cos^2 a = 1/2 + 1/2(cos^2 a-sin^2a)

cos^2 a = 1- sin^2 a
= 1/2 + 1/2 - (2sin^2 a)/2
= 1/2 + 1/2( 1- 2 sin^a)
= 1/2 + 1/2(1 - sin^2 a - sin^2 a)
= 1/2 + 1/2(cos^2 a - sin^2 a)


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