## Algebra 2 (1st Edition)

$t\approx 1.68$
Write height function. $h=-16t^{2}+h_{0}\qquad$ ...Substitute $0$ for $h$ and $45$ for $h_{0}$ $0=-16t^{2}+45\qquad$ ...add $16t^{2}$ to each side $16t^{2}=45\qquad$ ...divide both sides of the expression with $16$ $t^{2}=\displaystyle \frac{45}{16}\qquad$ ...take square roots of each side. $t=\pm\sqrt{\frac{45}{16}}\qquad$ ...simplify $\displaystyle \sqrt{\frac{45}{16}}=\frac{\sqrt{9\cdot 5}}{\sqrt{16}}=\frac{3\sqrt{5}}{4}$ $\qquad$ ...since we are calculating time, we can discard the negative solution $t=\displaystyle \frac{3\sqrt{5}}{4}$ $t\approx 1.68$