Law: Starting from the term 1, the absolute value is equal to the number of terms, followed by two positive terms and two negative terms.

General formula to satisfy this law:

an=(√2)n×cos[(2n-3)π/4]

2.

The method is the same as 1 question.

Law: Starting from the term 1, the denominator is the number of terms, and the numerator is 1, followed by two negative terms and two positive terms.

General formula to satisfy this law:

an=(√2)cos[(2n+3)π/4]/n