申論題

4. (10 points) It is known that the definite integral I = from 0 to 1 can represent the volume of the solid formed by revolving the region bounded by the curve y = cos x and the lines y = 0, x = 0, x = about the y-axis.

(b) Iff(t) dt from 0 to x² equals x cos(x) for all real number x, calculate the value of f(4). (5 points)