If you have more than one question, you need to make separate posts.

From the link, we see that the graph has an amplitude of 3, it has half a cycle in 90 degrees and it starts the cosine graph at 135 degrees.

Since the horizontal compression of a sine or cosine graph is `k=360/T` , where T is the period of the graph, this means that with half a cycle in 90 degrees, the full cycle is 180 degrees.

`k=360/180=2`

Finally, the horizontal shift of the graph is 135 degrees.  This can now be combined into a single function:

`y=3cos(2(x-135))`

The equation of the graph is `y=3cos(2(x-135))` .