8. (10 分) Let u = x2y3exz, where x = s2 + t2, y = 2st and z = s ln t. Find = ?
7. (10 分)Find the volume of the solid generated by revolving about the x-axis the region bounded by the curve y =, the x-axis, and the lines x = 0 and x = 2.
6. (10 分) Prove that ln(1+x) =,-1<x ≤ 1.