Question

Determine cos sabendo que 2< < e = 3. Lembre-se de que 2 + cos2 = 1

Answer 1

$\boxed{\begin{array}{l}\sf sen(x)=\dfrac{3}{5}\implies sen^2(x)=\dfrac{9}{25}\\\sf cos^2(x)=\dfrac{25}{25}-\dfrac{9}{25}=\dfrac{16}{25}\\\sf cos(x)=-\sqrt{\dfrac{16}{25}}=-\dfrac{4}{5}\end{array}}$