Acute triangles contain 3 angles, of all which are less than 90 degrees.
\(180^{\circ} = 89^{\circ} + 80^{\circ} + x\)Given it's a triangle, what is the unknown angle when the other angles are 89 and 80 degrees?
\(180^{\circ} = 169^{\circ} + x\)
\(180^{\circ} - 169^{\circ} = 169^{\circ} - 169^{\circ} + x \)
\(11^{\circ} = x\)
All the angles are less than 90^{\circ}, so the triangle is, acute.
