a2-7a-9=0

Solution for a2-7a-9=0 equation:

a2-7a-9=0

We add all the numbers together, and all the variables

a^2-7a-9=0

a = 1; b = -7; c = -9;
Δ = b2-4ac
Δ = -72-4·1·(-9)
Δ = 85
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-\sqrt{85}}{2*1}=\frac{7-\sqrt{85}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+\sqrt{85}}{2*1}=\frac{7+\sqrt{85}}{2}
$