Find the roots of the given equation by completing the square: ax^2+bx+c=0
start this way:
x^2 + b/a x = -c
complete the square
x^2 + b/a x + (b/2a)^2=(b/2a)^2-c
(x+b/2a)^2=(b/2a)^2 -c
take the sqrt of each side...
x= -b/2a +- sqrt (b^2-4ac) /2a