7c2-2c-15=-c2

Solution for 7c2-2c-15=-c2 equation:

7c^2-2c-15=-c2

We move all terms to the left:

7c^2-2c-15-(-c2)=0

We add all the numbers together, and all the variables

7c^2-(-1c^2)-2c-15=0

We get rid of parentheses

7c^2+1c^2-2c-15=0

We add all the numbers together, and all the variables

8c^2-2c-15=0

a = 8; b = -2; c = -15;
Δ = b2-4ac
Δ = -22-4·8·(-15)
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-22}{2*8}=\frac{-20}{16}
=-1+1/4
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+22}{2*8}=\frac{24}{16}
=1+1/2
$