Hey,

since

y=mx+(-)

(a²m²+b²)

It contains

(those points put in equation

(p,q)[my alp and bet arent coming]

(q-m(p))²=a²m²+b².

find m1 and m2 from equation as(m1+m2) and m1m2

put in angle equation

 

Ps:lazy to type the whole thing.if you want or if you didnt understand please post.