Explanation:
the slope of a line is airways the ratio
y coordinate difference / x coordinate difference
evergreen going from one point on the line to another.
slope RQ :
we are going from R to Q (we could also go in the other direction with the same result) :
(3, -2) to (-2, 3)
x changes by -5 (from 3 to -2).
y changes by +5 (from -2 to 3).
the slope of RQ is therefore +5/-5 = -1.
slope RP :
(3, -2) to (0, -5)
x changes by -3 (from 3 to 0).
y changes by -3 (from -2 to -5).
the slope RP is therefore -3/-3 = 1.
-1 × 1 = -1
so, yes, they are perpendicular. that means the triangle is right-angled.