Question 1085682
{{{ax^2+bx+c=y}}}


{{{system(a*0^2+b*0+c=3,a*1^2+b*1+c=4,a*(-1)^2+b(-1)+c=-6)}}}


{{{system(c=3,a+b+c=4,a-b+c=-6)}}}, and already you have one of the variables solved.


{{{system(a+b+3=4,a-b+3=-6)}}}, two equations in two unknown variables, and you can continue from this...