Question

Find the missing side or angle.

Answer 1

Answer:

$a=4.1$

Step-by-step explanation:

The Law of Cosines is given as:

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

Plugging in given values, we get:

$a^2=4^2+2^2-2\cdot 4 \cdot 2\cos 78^{\circ},\\a^2=16+4-16\cos 78^{\circ},\\a^2\approx \sqrt{16.673},\\a\approx \fbox{ 4.1 }$.