1) cot0= -7/2, cos0

should be equal to right?

Or you mean ?

If yes, then

By Pythagorous Theorem, you can get .

will be -ve when II and IV quadrants.

2) tan=1(1)

Where is the reference angle for your tangent?

3) sin-1(1)

Do you mean ?

If yes,

From the graph of sine, the angle should be