3a(a-5)=0

Solution for 3a(a-5)=0 equation:

3a(a-5)=0

We multiply parentheses

3a^2-15a=0

a = 3; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·3·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*3}=\frac{0}{6}
=0
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*3}=\frac{30}{6}
=5
$