$\begin{array}{1 1}(a)\;e=\sqrt{1+\big(\large\frac{b}{a}\big)}\\(b)\;e=\sqrt{1+\big(\large\frac{a^2}{b^2}\big)}\\(c)\;e=\sqrt{1-\big(\large\frac{b^2}{a^2}\big)}\\(d)\;e=\sqrt{1+\big(\large\frac{b^2}{a^2}\big)}\end{array}$
