9514 1404 393
Answer:
A. no
B. no
C. obtuse
Step-by-step explanation:
For side lengths to form a triangle, the sum of the shorter two must exceed the longest.
A. 5 + 8 = 13 . . . . a line segment, not a triangle
B. 7 + 12 < 26 . . . . no closure, not a triangle
C. 11 + 15 > 20 . . . . a triangle. A picture shows it to be obtuse
You can also compare 11² +15² vs 20² ⇒ 346 vs 400. The long side is too long for a right triangle, so the triangle must be obtuse. (The Pythagorean theorem tells you a right triangle with those legs would have a long side of √346 = 18.6.)
