(4k+5k)(k+7)=0

Solution for (4k+5k)(k+7)=0 equation:

(4k+5k)(k+7)=0

We add all the numbers together, and all the variables

(+9k)(k+7)=0

We multiply parentheses ..

(+9k^2+63k)=0

We get rid of parentheses

9k^2+63k=0

a = 9; b = 63; c = 0;
Δ = b2-4ac
Δ = 632-4·9·0
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(63)-63}{2*9}=\frac{-126}{18}
=-7
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(63)+63}{2*9}=\frac{0}{18}
=0
$