Final answer:
The length of the third side of the isosceles triangle is 17cm.
Step-by-step explanation:
To find the length of the third side of an isosceles triangle, we need to subtract twice the length of the equal sides from the perimeter. In this case, the perimeter is 45cm and each of the equal sides is 14cm long.
So, the length of the third side is 45cm - 14cm - 14cm = 17cm.