In order for the triangle to be called an isosceles right triangle, it must satisfy both conditions: XZ and XY must be perpendicular to each other, and XZ = XY. To determine whether two lines are perpendicular, their slopes must be negative reciprocals of each other.
Solving for the slopes of XZ and XY: slope of XZ = (y₂-y₁) / (x₂-x₁) = (6-3)/(5-1) = 3/4 slope of XY = (y₂-y₁) / (x₂-x₁) = (3--1)/(1-4) = -4/3 -4/3 is the negative reciprocal of 3/4, therefore XZ and XY are perpendicular to each other.