try to find the distance AB, BC and CA, then all you got to do is add them up.

Formula is square root of {(x2-x1)^2 + (y2-y1)^2}

which has come from the Pythagorean theorem. (A^2 = B^2 + C^2)

So, let’s find the distance.

distance of AB – A(3, 1), B(-1, 1)

sqrt{(-1 – 3)^2 + (1 – 1)^2} = sqrt {(-4)^2 + 0^2} = sqrt 16 = 4

distance of BC – B(-1, 1), C(-1, -2)

sqrt[{(-1) – (-1)}^2 + ((-2) – 1)^2] = sqrt{(0^2)+(-3)^2} = sqrt 9 = 3

distance of CA – C(-1, -2), A(3, 1)

sqrt[{3 – (-1)}^2 + {1 – (-2)}^2] = sqrt {(4)^2 + (3)^2} = sqrt 25 = 5

As you can see from above, distance of AB, BC and CA are 4, 3, 5. Now add them up to find the length if the sides of triangle ABC which is equal to 12.

there u go.

you will then have a triangle