7(3x+5)x=700

Solution for 7(3x+5)x=700 equation:

7(3x+5)x=700

We move all terms to the left:

7(3x+5)x-(700)=0

We multiply parentheses

21x^2+35x-700=0

a = 21; b = 35; c = -700;
Δ = b2-4ac
Δ = 352-4·21·(-700)
Δ = 60025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{60025}=245$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(35)-245}{2*21}=\frac{-280}{42}
=-6+2/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(35)+245}{2*21}=\frac{210}{42}
=5
$