Find Third point of Triangle

Hi Every one

i want to find third Point of Triangle
i Have two point p1,p2 with respect to it i want to find third point of triangle

Note one thing triangle is 45 - 90 - 45 degree so the point i want to find is at 90 degree,

so as per my requirment
p1 = 45 degree
p2 = -45 degree
and p3 = 90 degree

so i want to find p3

any help will gtreatly appreciated to me
i havwe attached image for further refrence