Find the value of tan (-945) degrees?

When I get a question like this I like to transform it into a positive angle as I think it's easier to work with. If you add 360° on to the angle, the trig values stay exactly the same.

tan (-945) ° = tan (-585) ° = tan (-225) ° and so on ...

keep doing this until you get a positive value, in our case we get tan (135) °

This is in the second quadrant of a unit circle diagram so we know tan must be negative and make an angle of 45° to the x-axis so tan (135) °=-tan (45) °

tan (45) ° = 1 therefore combining all this gives tan (-945) ° = - 1.

(I know there's a lot to take in there, if you have any questions, feel free to ask.)