6. Numerical calculations

f1 = Expand[(s - 1) (s - 3) (s - 5)]

Factor[f1]

Solve[f1 == 0, s]

f2 = x  - 2 Sin[λ x]  /.  λ -> Pi

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

FindRoot[ f2 == 0, {x, 1}]