Coterminal angles are angles in standard position (angles with the initial side on the positive x-axis) that have a common terminal side.
In another words, are angles "located at the same place". We can find coterminal angles by adding or subtracting 2π from our angle.
First, let's add 2π.
[tex]-\frac{7\pi}{4}+2\pi=-\frac{7\pi}{4}+\frac{8\pi}{4}=\frac{-7\pi+8\pi}{4}=\frac{\pi}{4}[/tex]
π/4 is a positive angle that is coterminal to -7π/4.
Now, let's subtract 2π.
[tex]-\frac{7\pi}{4}-2\pi=-\frac{7\pi}{4}-\frac{8\pi}{4}=\frac{-7\pi-8\pi}{4}=-\frac{15\pi}{4}[/tex]
-15π/4 is a negative angle that is coterminal to -7π/4.
