False Position (Linear Interpolation) Numerical Method

% Inputs: with examples
% AF = anonymous function equation: AF = @(x) 1-((20^2)./(9.81*(((3*x)+((x.^2)/2)).^3))).*(3+x);
% xb = initial guess x bracket = [xL xU], where xL = lower boundary x and xU = upper boundary x: xb = [0 2.5];
% ed = desired approximate relative error = |(current - previous)/current|: ed = 0.01;
% Outputs
% xR = x root
% err = approximate relative error
% n = number of iterations
% xRV = x root vector
% errV = approximate relative error vector
% AFD1 = anonymous function 1st derivative
% AFD2 = anonymous function 2nd derivative