1. This shape comes in scalene, equilateral, or 15-Down varieties (8)
3. Angle greater than 90 degrees and less than 180 degrees is this (6)
4. Longer dimension of a rectangle (6)
5.  ____ sign, +, is used in addition (4)
6. Sharing a pie between friends requires this kind of operation (8)
8. No Clue
11. To determine the product (8)
14. A gram, a foot or 87 degrees (7)
15. A three-sided figure having two equal sides (9)
16. The answer in a division problem (8)
17. A quadrilateral with four sides equal (6)
19. An angle measuring less than 90 degrees (5)