What is the measure of angle A in the triangle?

Determine which expressions represent real numbers and which expressions represent complex number. asaaap! plis!

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?

Given: δabc, m∠1=m∠2, d∈ ac bd = dc m∠bdc = 100º find: m∠a m∠b, m∠c