% trapezoid Composite trapezoid's rule
% Output: I = approximate value of the integral from a to b of f(x)*dx

n = 5;    % input total number of nodes
a = 8;     % input lower limit
b = 30;    % input upper limit
h = (b-a)/(n-1);     %  stepsize
x = a:h:b;           %  divide the interval
fun = 2000*ln(140000./(140000-2100*x))-9.8*x; % input function


f = eval("fun");    %  evaluate integrand

% output
I = h * ( 0.5*f(1) + sum(f(2:n-1)) + 0.5*f(n) );
write("I = ",I);