Question

How do you determine the two coterminal angle (one positive one negative) for the angle `-420^circ`?

Answer 1

There are a countably infinite number of angles coterminal to `-420^circ;` we're free to add or subtract `360^circ` as many times as we like to come up with them. Adding once gives our negative answer, `-60^circ` and once more our positive answer, `300^circ.`