how to know when to use c2=a2+b2 or a2+b2=c2 in a question that doesnt have a shape

Step-by-step explanation:
A flagpole is 53 feet tall. Most of the time, this will be a vertical side of the triangle.
The flagpole and the ground are perpendicular to each other so they should form the legs of the triangles, this the triangle will be a right angle.
The rope will be the hypotenuse, the side opposite of the right angle.