(4b+3)(b+7)=0

Solution for (4b+3)(b+7)=0 equation:

(4b+3)(b+7)=0

We multiply parentheses ..

(+4b^2+28b+3b+21)=0

We get rid of parentheses

4b^2+28b+3b+21=0

We add all the numbers together, and all the variables

4b^2+31b+21=0

a = 4; b = 31; c = +21;
Δ = b2-4ac
Δ = 312-4·4·21
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(31)-25}{2*4}=\frac{-56}{8}
=-7
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(31)+25}{2*4}=\frac{-6}{8}
=-3/4
$