The Cosine Rule (VCE SSCE General Mathematics): Flashcards

Any triangle (non-right-angled)

Two sides and the included angle

All three sides

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

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

Opposite the longest side

Angle $A$ is obtuse (between 90° and 180°)

Becomes Pythagoras' theorem ($\cos 90° = 0$)

Clockwise from North

Three-figure numbers (e.g., 037° not 37°)