First find the common ration, then multiply the last given number by the common ratio.
To get the common ration, divide the second sequence by the first, then the third by the second, then the fourth by the third.
-1/1 = -1 (divide second sequence by the first)
1/-1 = -1 (divide third sequence by the second)
-1/1 = -1 (divide fourth sequence by the third)
The common ratio is -1.
Multiply the last given sequence by the common ratio -1 to get the next sequence.
(-1) x (-1) = 1The fifth sequence is 1.
To use the geometric sequence formula:
n = 5 (the fifth sequence)
a₁ = 1 (first sequence)
r = -1 (common ratio)