Let f be the function defined on [0,3] by: For e ]0, 1[, we define the partition 1) Find the upper sum U(f. P.) and the lower sum L(f, Pe). 2) Show that the lower integral L(f) and the upper integral U(f) satisfy: L(f)=U(f) = 2 3) Conclude that f is Darboux integrable and evaluate [²₁ 1, -1, 2, if 0 ≤ x ≤ 1 if 1 < x≤2 f(x) = if 2