Chapter 1 - Equations and Inequalities - Exercise Set 1.4 - Page 143: 80

$-5$

$\frac{-b-\sqrt (b^{2}-4ac)}{2a}$ Substitute $a=2, b=9$ and $c=-5$ $\frac{-b-\sqrt (b^{2}-4ac)}{2a} $$= \frac{-9-\sqrt (9^{2}-4(2)(-5))}{2(2)}$ $= \frac{-9-\sqrt (81+40)}{4}$ $= \frac{-9-\sqrt 121}{4}$ $= \frac{-9-11}{4}$ $= \frac{-20}{4}$ $=-5$