Help me please this is due today help me

Which math sentence can be used to determine if the triangle is a right triangle?

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

Car a and car b were in a race .the driver of car b claimed that his car was twice as fast as car a