Form the perfect square trinomial in the process of completing the square. what is the value of c?

x2 + 3x + c = startfraction 7 over 4 endfraction + c

c =

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?