Question 1206854
{{{ax^2+bx+c=0}}}

{{{ax^2+bx=-c}}}
{{{a(x^2+(b/a)x)=-c}}}
If you were to make a graphical representation, you could arrange the parts so 
would appear a missing square piece....

{{{x^2+(b/a)x=-c/a}}}

{{{x^2+(b/a)x+(b/(2a))^2=(b/(2a))^2-c/a}}}

{{{(x+b/(2a))^2=b^2/(4a^2)-(4ac)/(4a^2)}}}

{{{(x+b/(2a))^2=(b^2-4ac)/(4a^2)}}}

{{{x+b/(2a)=0+- (b^2-4ac)/(2a)}}}

{{{highlight_green(x=-b/(2a)+- (b^2-4ac)/(2a))}}}


You equation assigned a=2,  b=-9, c=5.