How do you verify $Cos(180° - theta) = -cos theta$ ?

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Answer 1 · 2016-05-23T09:47:32

Please see below.

One of the easiest ways could be to use the formula

$cos(A-B)=cosAcosB+sinAsinB$

Hence, $cos(180^o-theta)=cos180^ocostheta+sin180^osintheta$

= $(-1)xxcostheta+0xxsintheta$

= $-costheta$

How do you verify Cos(180° - theta) = -cos thetaCos(180° - theta) = -cos theta?