True or False, The value pi/12 is a solution for the equation 4 cos^2(4x)-3=0

Please explain

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

Which best explains why this triangle is or is not 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?