Cosine Rule (Leaving Cert Mathematics): Quizzes

Two sides & included angle

All three side lengths

$a^2=b^2+c^2-2bc\cos A$

$\cos A=\frac{b^2+c^2-a^2}{2bc}$

The angle between two given sides

$A$ is opposite side $a$

$4.74$ m

$72.97°$

To find an angle from its cosine value

$\cos A=\frac{b^2+c^2-a^2}{2bc}$