% actual value given by the textbook
exact = -1.99899998;

% excute h1_11b & h1_11c to get answer_b
% and answer_c
h1_11b
h1_11c

% relative error = |p-p*|/|p| where p is the 
% exact solution and p* is an approximation to p
rel_1 = abs(exact-answer_11b)/abs(exact)
rel_2 = abs(exact-answer_11c)/abs(exact)
% rel_2 = abs(exact-(-2))/abs(exact)