Find the derivative using the limit process for any or all of these problems

Create and solve a linear equation that represents the model, where squares and triangles are shown evenly balanced on a balance beam. assume the weight of a square is 1 unit and the weight of a triangle is unknown.

Evaluate cos2θ for cosθ = square root of 3/2

Can somebody 1. what is the formula for finding the vertical distance between two points on a coordinate plane?