First@Solve[a x+b ==0,x]

First@Solve[a (x^2)+b x+c ==0,x]

First@Solve[a (x^3)+b (x^2)+c x+d==0,x]

First@Solve[a (x^4)+b (x^3)+c (x^2)+d x+e==0,x]

First@Solve[a (x^4)+b (x^3)+c (x^2)+d x+e==0,x]//TeXForm

Solve[a (x^4)+b (x^3)+c (x^2)+d x+e==0,x][[1,1,2]]

Solve[a (x^4)+b (x^3)+c (x^2)+d x+e==0,x][[1,1,2]]//Simplify

Solve[a (x^4)+b (x^3)+c (x^2)+d x+e==0,x][[1,1,2]] // FullSimplify