Question

How do you graph `y = -cos ( x- pi/4)`?

Answer 1

You can extract various information only by looking at your function:
1] It is a cosine;
2] the `-1` in front of it tells us that the amplitude is `1` and every time we evaluate the `cos` we have to change sign;
3] The `1` in front of `x` tells us that the period is `1=(2pi)/(period)`
and `period=2pi`;
4] `-pi/4` is the starting angle or initial phase that is the angle when `x=0`;