Matt W. answered • 04/04/19

Cornell Math and Science Tutor with Engineering Background

So sequences have a **common difference** between numbers. If the first number is 1 and then next the number is -1, then the common difference is -2.

In this case, we start with 1 (a_{0} means the zero number of the sequence). To find the next number in the sequence, a_{n}, we take the previous number, a_{n-1}, and subtract 2.

a_{0 }= 1

a_{n} = a_{n-1} - 2

Thus,

a_{0 }= 1

a_{1 }= -1

a_{2 }= -3

a_{3 }= -5

a_{4 }= -7

a_{5 }= -9