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How do you solve $-cosx=1+2cos(x-pi)$ ?

1 Answer

Oct 3, 2016

$S={2pin}$

Explanation:

$-cosx =1+2cos(x-pi)$ -> use formula $cos (A-B)=cosAcosB+sinAsinB$

$-cosx=1+2(cosxcospi+sinxsinpi)$

$-cosx=1+2(cosx*-1+sinx *0)$

$-cosx=1-2cosx$

$-cosx + 2cos x =1$

$cos x = 1$

$x=cos^-1 (1)$

$x=0+2pin = 2pin$

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