Find the sum of the GP :
1 – a + a2 – a3 + …to n terms ( a ≠ 1)
Sum of a G.P. series is represented by the formula, , when r≠1. ‘Sn’ represents the sum of the G.P. series upto nth terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms.
Here,
a = 1
r = (ratio between the n term and n-1 term)
n terms
∴
[ Multiplying both numerator and denominator by -1 ]
⇒