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Mathematics 18 Online
OpenStudy (anonymous):

expand or solve cos5x-cosx

OpenStudy (raden):

use the identity : cosA - cosB = -2sin[(A+B)]/2 * sin[(A-B)]/2

OpenStudy (raden):

here, let A=5x and B=x

OpenStudy (raden):

so, cos(5x) - cos(x) = -2 sin(5x+x)/2 sin(5x-x)/2 = -2 sin(3x) sin(2x)

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