y-7y=21y^2

Solution for y-7y=21y^2 equation:

y-7y=21y^2

We move all terms to the left:

y-7y-(21y^2)=0

determiningTheFunctionDomain
-21y^2+y-7y=0

We add all the numbers together, and all the variables

-21y^2-6y=0

a = -21; b = -6; c = 0;
Δ = b2-4ac
Δ = -62-4·(-21)·0
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-6}{2*-21}=\frac{0}{-42}
=0
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+6}{2*-21}=\frac{12}{-42}
=-2/7
$