(* 1º *)

Solve[a x^2+b x+c==0,x]

(* 2º *)

{2*3+4*5,(2+3)(4+5)}

(* 3º *)

ReplaceAll[{x,y},{x->2,y->3}]

(* 4º *)

Do [Print[i,"   ",i^3],{i,1,10}]

(* 5º *)

TableForm[Table[{i,i^3},{i,1,10}]]

(* 6º *)

?*Plot*

?Plot

(* 7º *)

Plot[Cos[x],{x,0,2Pi}]

Plot[Sin[x],{x,0,2Pi}]

(* 8º *)

Plot[Sin[x],{x,0,2Pi},PlotLabel->Sin[x],LabelStyle->Directive[Bold,Orange]]

(* 9° *)

Plot[{Sin[x],1-x/4},{x,-1,8}]

FindRoot[Sin[x]==1-x/4,{x,1}]

FindRoot[Sin[x]==1-x/4,{x,3}]

FindRoot[Sin[x]==1-x/4,{x,5}]