\[\eta=\frac{q_{1}-q_{2}}{q_{1}}=\frac{\left(h_{3}-h_{2}\right)-\left(h_{4}-h_{1}\right)}{h_{3}-h_{2}}=\frac{\left(h_{3}-h_{4}\right)-\left(h_{2}-h_{1}\right)}{h_{3}-h_{2}}\]
\[\eta=\frac{q_{1}-q_{2}}{q_{1}}=\frac{\left(h_{3}-h_{2}\right)-\left(h_{4}-h_{1}\right)}{h_{3}-h_{2}}=\frac{\left(h_{3}-h_{4}\right)-\left(h_{2}-h_{1}\right)}{h_{3}-h_{2}}\]