So we are looking for the diagonal line. So what you want to do is multiply 8 by 8 (always multiply it by its self) and 6 times 6. then add them together which would be 100. Then find the square root of 100. so the hypotenuse ( diagonal line) is 10. So checking if it is a right triangle is easy. all you do is multiply the legs (the straight up and down and left and right sides) by itself so 8 times 8 is 64 and 6 times 6 is 36. The 10 times 10=100 so the 2 legs added together should be the same as the hypotenuse ( diagonal line) to be a right angle.