10(!). The first number is \(a\), the second is \(b\), the third is the difference between the second and the first, the fourth is the difference between the third and the second, and so on. What number is in the 124th place?
10. Solution. The third number is \(b-a\), the fourth \(b-\) \(-a-b=-a\), the fifth \(-a-(b-a)=-b\), the sixth \(-b-(-a)=\) \(=a-b\), the seventh \(a-b-(-b)=a\), i.e., equal to the first number, the eighth \(a-(a-b)=b\), i.e., equal to the second number, and so on. The number at the \(124-\mathrm{th}\) position is equal to the fourth, i.e., \(-a\).