That is, 1: only one * * * line has four points, that is, c (4,3) = 4.

? 2. There are four 3-point * * * lines with level 4xc (3,3) = 4.

draw

2) Of the 100 pieces, 3 * * have a C (100,3). Among them, including C(97, 3), all three pieces have no defects.

So there is at least one defective product in C (100,3)-C (97,3). (negative consideration)

3) Any 3-point household line on the circle, so it can be made into c C( 10/0,2) = 45 strings.

It can be c C( 10/0,3) =120 triangles.

A triangle consisting of a chord passing through the center of the circle and any point on the circle is a right triangle. * * * There are five chords passing through the center of the circle, and each chord can make eight right-angled triangles, so one * * * can make 8X5=40 right-angled triangles.