eqn=x^2-3x + 2==0

Solve[eqn,x]

x^2 /.%2

eqn=9 x -3 == 4x+2

Solve[eqn,x]

Solve[x^3-2x^2-5x+6==0,x]

Solve[x^2+3x== x+7,x]

N[%]

eqn=(a-x) ((a-x)^3-2b^2 (a-x))-b (b (a-x)^2-b^3)==0

Solve[eqn,x]

N[%]

Expand[%]

eqn=x+3 Exp[-x]==3

Solve[eqn,x]

FindRoot[eqn,{x,3}]

Minimize[x^2-2x-1,x]

Maximize[-x^2+5x-3,x]