28. Find the volume of revolution V x of the plane figure A surrounded by the tangent at the curve y= 1-x2 and its point (1, 0) and the figure rotates around the X axis once.

29. Cut the wire of length A into two sections, one is square and the other is round. When you ask how many two sections of a wire are, the sum of the areas of a square and a circle is the smallest. V. Proof questions (10)

30. Given the function f (x) =e x -x -2, it is proved that there is at least one point X 0 in the interval, so that EX-X 0 = 2.