The least number of acute angles that a triangle can have is 2. Let imagine you had 1 acute angle and 2 other angles that were non-acute (90° or higher) a less than 90° b less than 90° c less than 90° All the angles in a triangle add up to 180° (i.e) a + b + c = 180° Since b and c are 90° or higher, that requires a to be negative. But we cannot have a negative angle, so there is no way to create a triangle with 1 (or fewer) acute angles.