# Math Help - Trigonometry

1. ## Trigonometry

Two sides of a paralellogram measure 7.0cm and 9.0cm. THe longer diagonal is 12 cm long. Calculate all the interior angles , to the nearest degree, of the paralellogram.

2. Do you know the Law of Cosines?

$c^2 = a^2 + b^2 - 2ab\cos(\theta)$, so
$12^2 = 7^2 + 9^2 - 2(7)(9)cos(\theta)$.

Solve that for $\theta$, and you have one angle, and its opposite. The other two angles are supplements of that angle ( $180 - \theta$).