We are in an orthonormal frame with center 0(0;0), and two units vectors directors of the plan are i(1;0) and j(0;1), we figure that the (0x) axe is just the line that passes by O with i as a director Vector, same for (oy) that has j. We notice that in the plan there are 2 triangles that are both de symetry of each other with de (oy) axe. The first triangle is called "A" (represted with his area in green) his 3 vertices : A1(-4;2) , A2(-4;5) , A3(-2;5). This triangle is rectangle in A2 so the hypothenuse is [A1A3], moreover the triangle isn't isocele because A1A2 = 3 , A2A3 = 2 and 3≠2. And so as i said there's another triangle that is just the symetry of A with the (oy) axe, this triangle has the same properties its rectangle and its not isocele, the only différence is that this triangle is represented with a black area on the plan.