Evaluate the Riemann sum for f(x) = 5 −1/2x, 2 ≤ x ≤ 14,with six subintervals, taking the sample points to be left endpoints.

Question

I don't understand

is the answer 18?

Answer 1

with left endpoints, then you want to evaluate f at
x = 2,4,6,8,10,12
so f(x) ≈ 2((5-2/2)+(5-4/2)+...(5-12/2))
= 2(4+3+2+1+0-1)
= 18