SOLUTION: If cos x = -1/5, find the value of cos(x+pi)

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Question 813220: If cos x = -1/5, find the value of cos(x+pi)
Answer by lwsshak3(11628) About Me  (Show Source):
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If cos x = -1/5, find the value of cos(x+pi)
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sinx=√(1-cos^2x)=√(1-1/25)=√(24/25)=√24/5
Identity: cos(a+b)=cosa*cosb-sina*sinb
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cos(x+π)=cosx*cosπ-sinx*sinπ=(-1/5*-1)-(√24/5*0)=1/5