Question

Solve by using the quadratic formula. Express the solution set in exact simplest form. y^2-7y-9=0

Answer 1

`~~~~~~~~~~~~\textit{quadratic formula} \\\\ \stackrel{\stackrel{a}{\downarrow }}{1}y^2\stackrel{\stackrel{b}{\downarrow }}{-7}y\stackrel{\stackrel{c}{\downarrow }}{-9}=0 \qquad \qquad y= \cfrac{ - b \pm \sqrt { b^2 -4 a c}}{2 a} \\\\\\ y= \cfrac{ - (-7) \pm \sqrt { (-7)^2 -4(1)(-9)}}{2(1)} \implies y = \cfrac{ 7 \pm \sqrt { 49 +36}}{ 2 } \\\\\\ y= \cfrac{ 7 \pm \sqrt { 85 }}{ 2 }\implies y= \begin{cases} \frac{ 7 + \sqrt { 85 }}{ 2 }\\[1em] \frac{ 7 - \sqrt { 85 }}{ 2 } \end{cases}`