How would you calculate the cosine of an obtuse triangle's largest angle?
Cos = adj/hyp. But which side is the adjacent side?
How would you calculate the cosine of an obtuse triangle's largest angle?
Cos = adj/hyp. But which side is the adjacent side?
Cosine=adjacent/hypotenuse is only true in right triangles, as that is the only time there is a hypotenuse. $\cos \theta$ is well defined for $\theta \gt 90^{\circ}$ and we have $\cos \theta=-\cos (180^{\circ}-\theta)$.
$\cos A= -\cos(180-A)$ e.g $\cos(120)= -cos(180-120)= -\cos60$ i.e $-1/2$ or $-0.5$