31. The three points $A, B$ and $C$ make a triangle and have the coordinates $A(-7,-8), B(-6,-13)$, and $C(-31,-8)$. What type of triangle is it?

Step 1 ：Given the coordinates of the three points A, B and C as A(-7,-8), B(-6,-13), and C(-31,-8).

Step 2 ：Calculate the lengths of the sides of the triangle using the distance formula \(d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\).

Step 3 ：The calculated lengths of the sides AB, BC and AC are approximately 5.10, 25.50 and 24.00 respectively.

Step 4 ：Since all sides are not equal, it is not an equilateral triangle.

Step 5 ：Since no two sides are equal, it is not an isosceles triangle.

Step 6 ：Since the square of the length of one side is not equal to the sum of the squares of the lengths of the other two sides, it is not a right triangle.

Step 7 ：Therefore, the triangle is a scalene triangle.

Step 8 ：Final Answer: The triangle is \(\boxed{\text{Scalene}}\) triangle.