Multiples of 90 (1 Viewer)

[od9895]

Hello
Could anyone please show me how to get rid of the multiples of 90 inside the bracket

1. cos (180 - x)
2. cos (720- x)
3.sin (- x)
4. sin (180 - 2x)
5. tan (180-3x)

Thanks

 

[deswa1]

Firstly, you know that you measure any angle from the x axis. Therefore cos(180-x) means x degrees in an clockwise direction from the x axis at 180 degrees. This is the same 'base' angle as x degrees. But cos is negative in the second quadrant. Therefore cos(180-x)=-cosx.

Does that make sense?