(4x+9)*(7x-4)=0

Solution for (4x+9)*(7x-4)=0 equation:

(4x+9)(7x-4)=0

We multiply parentheses ..

(+28x^2-16x+63x-36)=0

We get rid of parentheses

28x^2-16x+63x-36=0

We add all the numbers together, and all the variables

28x^2+47x-36=0

a = 28; b = 47; c = -36;
Δ = b2-4ac
Δ = 472-4·28·(-36)
Δ = 6241
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6241}=79$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(47)-79}{2*28}=\frac{-126}{56}
=-2+1/4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(47)+79}{2*28}=\frac{32}{56}
=4/7
$