A right triangle with a 90 degree angle. Also, for the question, use the Pythagoras theorem. a^2 + b^2 = c^2. Use the two smaller sides for a^2 + b^2 and the larger number for c^2. If they are equal on both sides, then it is a right triangle. For example on the first problem, 10^2 + 15^2 does not equal 20^2. Therefore, the answer would be no.
