given:
f(x) = 2-1/4 x
Evaluate the Riemann sum for 2 ≤ x ≤ 4 , with six subintervals, taking the sample points to be left endpoints.
Evaluate f(x) at x=2, 2 1/3, 2 2/3, 3, 3 1/3 and 3 2/3. Multiply each f(x) by the x subinterval (1/3) and add up the results.
The result will be an approximation to the integral of f(x) from 2 to 4.