Sentence:  In order to be an <WSD>acute</WSD> triangle, all three angles of a triangle must be "less" than 90°. These triangles can have very prickly personalities. So, if you want to create images of porcupines, rugged mountains, or narrow pine trees in your geometric design, you may best do it by using <WSD>acute</WSD> trianglesnb.... The most commonly used <WSD>acute</WSD> triangle in quiltmaking is the equilateral trianglenb.... All three of its angles are 60°. 
Meaning of the word marked with <WSD> tags:  Of a triangle: having all three interior angles measuring less than 90 degrees.