Question

Simplifique: cos140º.cos40º - sen140º.sen40º =

A
1
B
-1
C
1/2
D
0

Answer 1

$\Large\boxed{\begin{array}{l}\underline{\rm Cosseno~da~soma}\\\sf cos(a+b)\\\sf =cos(a)\cdot cos(b)-sen(a)\cdot sen(b)\end{array}}$

$\Large\boxed{\begin{array}{l}\sf cos(140^\circ)\cdot cos(40^\circ)-sen(140^\circ)\cdot sen(40^\circ)\\\sf\implies cos(140^\circ+40^\circ)\\\sf\implies cos(180^\circ)=-1\end{array}}$