21x^2-14x=x

Solution for 21x^2-14x=x equation:

21x^2-14x=x

We move all terms to the left:

21x^2-14x-(x)=0

We add all the numbers together, and all the variables

21x^2-15x=0

a = 21; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·21·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*21}=\frac{0}{42}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*21}=\frac{30}{42}
=5/7
$