Answer:56.8 inches
Step-by-step explanation:
For perimeter we must find the lengths of the 2 diagonal sides of the triangle which are the same because it is isosceles.
the triangle is cut directly in half so both halves of the base are 17/2
17/2 = 8.5
solve through pythagoren theorum
altitude^2 + (half of base)^2 = (diagonal length)^2
18^2 + (8.5)^2 = (diagonal length)^2
324 + 72.25 = (diagonal length)^2
396.3 = (diagonal length)^2
= diagonal length
diagonal length = 19.9
diagonal length + diagonal length + base = perimeter
19.9 + 19.9 + 17 = perimeter
56.8 inches = perimeter