An illustration showing an angle the is less than a right angle. This is an acute angle.

"Argent, a fusil, purpure. The fusil is narrower than the lozenge, the angles at the chief and base…

Illustration of an angle &alpha with the vertex at the center, O, of a circle with radius OB. AC and…

Illustration of an angle &alpha with the terminal side used to draw a triangle in quadrant I.

Illustration showing an acute triangle (one that has all three angles that are acute).

Illustration showing an equiangular triangle (one that has all three angles that are equal).