The answer depends on the information that you do have. There are many different methods.
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Its not a triangle if it has only two sides.
You find the three sides of the triangle, and assure that they are all in the same unit, and then add the sides together to find the perimeter of the triangle.
By using sides we get area of triangle and then using (1/2)heightxbase we get height.
Find the perimeter by adding the lengths of the sides
The midpoint of a triangle is the 3rd sides' size, divided by 2.