Problem 2: Estimate the area under the graph off(x) = 4 cos(x) fromx = 0 tox =π/2. (Round the answer to four decimal places.)(a) Use four approximating rectangles and right endpoints.

My work and answer (which is wrong according to the site)

Delta x= Pi/2 / 4 = pi/8

R4= pi/8 (3.8+3.4+2.5+1.6)

R4= 4.4375

(b) b) Use four approximating rectangles and left endpoints.

L4= pi/8 f(pi/8) + pi/8 f(pi/4) +pi/8 f(3pi/4)

L4= pi/8 (4 + 3.9 +3.3 + 2.7)

L4=5.4585

I made a graph so these values are my estimates