How can i solve the indef. Integral 4Cos[4x]Cos[x]dx Or, maybe which identities does this involve? Thanks!
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Originally Posted by haydenr How can i solve the indef. Integral 4Cos[4x]Cos[x]dx Or, maybe which identities does this involve? Thanks! Use the trig identity: 2cos(A)cos(B) = cos(A+B) + cos(A-B) on the integrand to get: Int 4 cos(4x) cos(x) dx = Int 2 cos(5x) dx + Int 2 cos(3x) dx RonL