Explanation
3, -6, +12, -24
a = 3, r = -2
8n=a(1−rn)/1−r. ∴1−28=3(1−(−2n-1))/1−(−2). 1−28=3(1−(−2n-1))/3
1-28 = 1-(-2)n-1
-228 = -2n-1
8 = n-1
n = 9
3, -6, +12, -24
a = 3, r = -2
8n=a(1−rn)/1−r. ∴1−28=3(1−(−2n-1))/1−(−2). 1−28=3(1−(−2n-1))/3
1-28 = 1-(-2)n-1
-228 = -2n-1
8 = n-1
n = 9