Does anyone know the bottom one ?

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?

Proving the parallelogram diagonal theoremgiven abcd is a parralelogam, diagnals ac and bd intersect at eprove ae is conruent to ce and be is congruent to de

What is the angle measure, or angle of depression, between this bird and the bird watcher?