WILL GIVE BRAINLIEST - Can someone please do this and explain?

What is the length of the segment joining the points at (4,5) and (6,-2) round to the nearest tenth if necessary

Which of the following is the result of expanding the series

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?