2、log2 3=a，→lg3/lg2=a - ( 1)，log3 7=b→lg7/lg3=b - (2)

( 1)*(2):lg7/lg2=ab

log 14 56 = lg56/LG 14 =(lg7+3lg 2)/(lg2+lg7)

=(3+lg7/lg2)/( 1+lg7/lg2)=(3+ab)/( 1+ab)

3, solution1:15+8+14 = 37, 9 people, 9-3-3=3, no one participates in three competitions at the same time, so there are three people participating in track and field and ball games at the same time. No one participated in three competitions at the same time, 15 people participated in the swimming competition.

Another solution: suppose x people take part in track and field and ball games at the same time.

Participating in individual swimming competitions are:15-3-3 = 9;

Participate in individual track and field competition: 8-3-X=5-X

Participate in individual ball games:14-3-x =11-x.

Participate in three competitions: 0

Total population: 9+(5-x)+(11-x)+3+3+x+0 = 28.

The solution is X=3.

There are 9 people participating in the individual swimming competition.