2a^2-18a+28=0.

Solution for 2a^2-18a+28=0. equation:

2a^2-18a+28=0.

a = 2; b = -18; c = +28;
Δ = b2-4ac
Δ = -182-4·2·28
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-10}{2*2}=\frac{8}{4}
=2
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+10}{2*2}=\frac{28}{4}
=7
$