Question

Question:
gyazo.com/c8fe92564a8387ffc127233f6ad989a9

My work:
gyazo.com/27caca9994d03409268162130c61ce08
(I understand how to do trapezoidal approximation, but how would I go bout this while using only 4 sections?)

Answer 1

I realize I put 30 instead of 15. so the answer would actually be 2205!
When you solve using only 4 sections do you just ignore the other ones??

((f(0)+f(30))/2 * Δx) + ((f(30)+f(60))/2 * Δx) + ((f(60)+f(90))/2 * Δx) + ((f(90)+f(120))/2 * Δx)
(Δx)/(2) (f(0) + 2(f(30) + 2(f(60) + 2(f(90) + (f(120)
(30/2) (0+36 + 38 + 48 + 12)
A = 2010ft^2

Answer 2

You need to use 30, since you must cover the interval [0,120] with 4 subintervals. It just means that you use 2 width-15 intervals for each of your width-30 ones.

Your work looks good to me.