How would I find X? I tried using a2 + b2 =c2 but nothing worked

List x1, x2, x3, x4 where xi is the left endpoint of the four equal intervals used to estimate the area under the curve of f(x) between x = 4 and x = 6. a 4, 4.5, 5, 5.5 b 4.5, 5, 5.5, 6 c 4.25, 4.75, 5.25, 5.75 d 4, 4.2, 5.4, 6

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)

Hi i’m not sure how to do question 20 if u could explain how to do it that’d b great