EXPLANATION
Considering the equation x^2 + y^2 + 4x = 0
As we already know, the circle equation with a radius r, centered at (a,b) is:

Rewrite x^2 + y^2 + 4x = 0 in the form of the standard circle equation:
Group x-variables and y-variables together:

Convert x to square form:

Convert to square form:

Refine 4:

Rewrite in standard form:

Therefore the circle properties are:
center: (a,b)=(-2,0) radius: r=2
Finally, drawing the graph of the equation: