Parallelogram (point coordinates, diagonal, angle, straight line)

Hey guys! I will not be too long in pre-explanations - my cousin has big problem with math, however, i could not help him with this one. Hope you will.

**Task.** Given parallelogram's PRST three points R, S, T:

a) Calculate coordinates of a point P and construct parallelogram;

b) Write an equation of diagonal PS;

c) Calculate angle between diagonal PS and ST;

d) Write an equation for a line, which goes through centre of parallelogram and perpendicular to PS.

If you guys could also tell me what theory you used, that would be very much appreciated because i want to learn, not just get an answer. BIG BIG thanks!

Re: Parallelogram (point coordinates, diagonal, angle, straight line)