15=7w^2-15w

Solution for 15=7w^2-15w equation:

15=7w^2-15w

We move all terms to the left:

15-(7w^2-15w)=0

We get rid of parentheses

-7w^2+15w+15=0

a = -7; b = 15; c = +15;
Δ = b2-4ac
Δ = 152-4·(-7)·15
Δ = 645
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$w_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$w_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$w_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-\sqrt{645}}{2*-7}=\frac{-15-\sqrt{645}}{-14}
$
$w_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+\sqrt{645}}{2*-7}=\frac{-15+\sqrt{645}}{-14}
$