Question

calcule o valor de cos (pi + x)

Answer 1

$cos(a + b) = cos(a)*cos(b)-sen(a)*sen(b)$

$(\pi)rad=180^{0}$
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$cos(\pi +x)=cos(180^{0}+x)$
$cos(\pi +x)=cos180^{0}*cos(x)-sen180^{0}*sen(x)$
$cos( \pi +x)=(-1)*cos(x)-0*sen(x)$
$cos( \pi +x)=- cos(x)$