A triangle has side lengths of 18cm, 80 cm, and 81 cm. Classify is acute, obtuse, or right.
Put the two smaller sides into the Pythagorean Theorem to see what length the hypotenuse would be if it were a right triangle. (I get 82 cm.) Since the third side is only 81 cm, that means the angle across from it isn't quite oƿє-ṅєd up to 90 degrees. (Smaller sides mean smaller angles across from them.) The triangle is acute.
If the third side was greater than 82, the triangle would be obtuse.
18^2 + 80^2 = 6724
81^2 = 6561
18^2 + 80^2 > 81^2