Question

sabendo que 180° < B < 270° e cos B= -√2/2 determine B

Answer 1

$\displaystyle \text{cos B}=\frac{-\sqrt{2}}{2} \ \ ;\ \ 180^\circ<\text B<270^\circ \\\\ \text{cos B}= \text{cos}(225^\circ) = \frac{-\sqrt{2}}{2} \\\\ \underline{\text{Portanto}}: \\\\\ \huge\boxed{\text B = 225^\circ}\checkmark$