Question
Solve using formula.
5x2 + 13x + 8 = 0
5x2 + 13x + 8 = 0
✓
Answer
$\begin{array}{l}5 x ^2+13 x +8=0 \text { compare with } ax ^2+ bx + c =0 \\ \Rightarrow a =5, b =13 \text { and } c =8 \\ \therefore b ^2-4 ac =13^2-4(5)(8) \\ =169-160 \\ =9 \\ x =\frac{-b \pm \sqrt{ b ^2-4 ac }}{2 a } \\ \Rightarrow x =\frac{-13 \pm \sqrt{9}}{2 \times 5}\end{array}$
$\begin{array}{l}\Rightarrow x=\frac{-13 \pm 3}{10} \\ \Rightarrow x=\frac{-13+3}{10} \text { or } x=\frac{-13-3}{10} \\ \Rightarrow x=\frac{-10}{10} \text { or } x=\frac{-16}{10} \\ \Rightarrow x=-1 \text { or } x=-\frac{8}{5}\end{array}$
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