7x(7x-3)=0

Solution for 7x(7x-3)=0 equation:

7x(7x-3)=0

We multiply parentheses

49x^2-21x=0

a = 49; b = -21; c = 0;
Δ = b2-4ac
Δ = -212-4·49·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-21}{2*49}=\frac{0}{98}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+21}{2*49}=\frac{42}{98}
=3/7
$