Have the following question:

1) This question deals with the upper half plane, points are represented by complex numbers.

Let L denoted the h-line given by Re(z)=0

Let M be given by the semi-circle with centre 0 and radius 2

Let N be given by the semi-circle with centre -3 and radius 4

i) Find

L intersect N=A

N intersect M=C

L intersect M=B

I have found these fine im just having trouble with the next bit, i have the intersections as A(0,root7), B(0, 2), C(-0.5, root15/2)

The next part asks:

What is the value of the angle between the hyperbolic arcs BC and BA at B? And show that the angle between the hyperbolic arcs at CA and CB is tan(theta)=(3root15/11)?

I was thinking of finding the slopes at the intersection points, hence with the first one we have a vertical h-line therefore one of our angles would be pie/2, then using the slope at at "M" in respect to intersection B, hence having tan(\theta )=0?

Any help would be most appreciated.