CuA set is the complement of a set about U set. That is, if u = {1, 2,3,4,5} and a = {1, 2), then cua = {3,4,5). This must ensure that u contains a.

therefore

1.CuA={x|x is a triangle but not an acute triangle} is understood as CuA={x|x is a right triangle and an obtuse triangle};

Similarly, CuB={x|x is a triangle but not an isosceles triangle}

2.a∩B = { x | 1 & lt； x & lt3}; a∪B = { x | x & lt； -4 or x & gt-2};

So Cu (a ∩ b) = {x | x

2. This can be solved by Wayne diagram, reference books or primary school knowledge (there is such a problem in the Olympiad in primary schools).

Using primary school knowledge:

All participants:15; Only take part in mathematics: 30-15 =15; Only take part in physics 26-15 =11;

so * * *: 15+ 15+ 1 1 = 4 1；

So those who didn't participate in the activity: 50-41= 9;

However, I personally recommend Wayne diagram, because it is intuitive and it is not easy to make mistakes when encountering a slightly difficult problem.