(1) According to the meaning of the question, the number in the fifth line can be deduced as follows: 1 5, 10, 1 5,1.

(2)(a+b)5=(a+b)3(a+b)2

= a5+5a4b+ 10 a3 B2+ 10 a2 B3+5ab 4+b5，

(3)(a-b)5=(a-b)3(a-b)2

=(a3-3a2b+3ab2-b3)(a2-2ab+b2)

= a5-5a4b+ 10a3b 2- 10a2b 3+5ab 4-b5。

So the answers are 1, 5, 10, 10, 5, 1.