Degrees:

Add or subtract multiples of 360° to the original angle.
Adding 360° rotates the angle a full circle and lands you in the same spot. Subtracting 360° does the same thing in the opposite direction.

Example: Find a coterminal angle of 45°.

Add 360°: 45° + 360° = 405°

Subtract 360°: 45°  360° = 315° (negative angles are also valid)
Radians:

Add or subtract multiples of 2π to the original angle.
Similar to degrees, adding 2π rotates the angle a full circle. Subtracting 2π achieves the same effect in the opposite direction.

Example: Find a coterminal angle of π/3 radians.

Add 2π: π/3 + 2π = (7π)/3

Subtract 2π: π/3  2π = 5π/3 (negative angles are also valid)
Key points to remember:

You can find multiple coterminal angles by adding or subtracting multiples of 360° (or 2π) as many times as needed.

Coterminal angles have the same trigonometric values (sine, cosine, tangent).