-3x^2+15x+3=0

Solution for -3x^2+15x+3=0 equation:

-3x^2+15x+3=0

a = -3; b = 15; c = +3;
Δ = b2-4ac
Δ = 152-4·(-3)·3
Δ = 261
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{261}=\sqrt{9*29}=\sqrt{9}*\sqrt{29}=3\sqrt{29}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-3\sqrt{29}}{2*-3}=\frac{-15-3\sqrt{29}}{-6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+3\sqrt{29}}{2*-3}=\frac{-15+3\sqrt{29}}{-6}
$