a^2-11a-1=28=a

Solution for a^2-11a-1=28=a equation:

a^2-11a-1=28=a

We move all terms to the left:

a^2-11a-1-(28)=0

We add all the numbers together, and all the variables

a^2-11a-29=0

a = 1; b = -11; c = -29;
Δ = b2-4ac
Δ = -112-4·1·(-29)
Δ = 237
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{-(-11)-\sqrt{237}}{2*1}=\frac{11-\sqrt{237}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-11)+\sqrt{237}}{2*1}=\frac{11+\sqrt{237}}{2}
$