~20 Estimate I = (Ox - 8x2) dac using midpoints and n = 3 subintervals. 8 I~5 2 Estimate I = + 5 ) dx using n = 4 subintervals and (a) Left endpoints. I~ (b) Right endpoints. I~Using the method of substitution, I = V7x + 6 dx = f(u) du a where u= du = dx a = b = and f (u) = The value of the original integral is I =