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blsea [12.9K]
3 years ago
11

Cos4x = 8 cos^4 x - 8 cos^2 x + 1Please help me prove! :D 

Mathematics
1 answer:
sesenic [268]3 years ago
3 0
From cos(2x) = 2cos^2(x) -1

cos(4x) = 2[cos(2x)]^2 -1
= 2[2cos(x) -1]^2 -1
= 2[4cos^2(x) - 4cos(x) + 1] -1
= 8cos^2(x) - 8cos(x) + 1
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