cosh x ex e x 2 a Sketch the graphs of the functions y e and y y 3 y cosh x 2 y BES 3 2 1 y 2 2 3 2 1 cosh x y 2 1 2 3 y 3 y cosh x 2 y 2 ex on the same axes and use graphical addition see Section 2 7 to sketch the graph of y cosh x y 3 y cosh x 2 b Use the definition to show that cosh x cosh x e x 1 2 3 X X 3 y 2 y 2 2 1 3 2 1 18 y 1 1 3 y cosh x 2 2 2 2 3 1 2 3 X X