9(7k+8)(k-10)=

Solution for 9(7k+8)(k-10)= equation:

9(7k+8)(k-10)=

We move all terms to the left:

9(7k+8)(k-10)-()=0

We add all the numbers together, and all the variables

9(7k+8)(k-10)=0

We multiply parentheses ..

9(+7k^2-70k+8k-80)=0

We multiply parentheses

63k^2-630k+72k-720=0

We add all the numbers together, and all the variables

63k^2-558k-720=0

a = 63; b = -558; c = -720;
Δ = b2-4ac
Δ = -5582-4·63·(-720)
Δ = 492804
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{492804}=702$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-558)-702}{2*63}=\frac{-144}{126}
=-1+1/7
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-558)+702}{2*63}=\frac{1260}{126}
=10
$