cos2(a-π/3)=2cos^2(a-π/3)-1?

This equation holds
According to the double angle formula:
cos2a=(cosa)^2-(sina)^2
According to (COSA) ^ 2 + (Sina) ^ 2 = 1, that is, (Sina) ^ 2 = 1 - (COSA) ^ 2
Cos2a = 2 (COSA) ^ 2-1
We can get it by replacing a with a - π / 3
cos2(a-π/3)=2[cos(a-π/3)]^2-1
(it's hard to edit a formula)

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