<P> An acute triangle is a triangle with all three angles acute (less than 90 °). An obtuse triangle is one with one obtuse angle (greater than 90 °) and two acute angles . Since a triangle's angles must sum to 180 °, no triangle can have more than one obtuse angle . </P> <P> Acute and obtuse triangles are the two different types of oblique triangles--triangles that are not right triangles because they have no 90 ° angle . </P>

A triangle with one obtuse angle must have two acute angles