3a^2+15a=18

Solution for 3a^2+15a=18 equation:

3a^2+15a=18

We move all terms to the left:

3a^2+15a-(18)=0

a = 3; b = 15; c = -18;
Δ = b2-4ac
Δ = 152-4·3·(-18)
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-21}{2*3}=\frac{-36}{6}
=-6
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+21}{2*3}=\frac{6}{6}
=1
$