Infinite arithmetico–geometric series (Sum of (a+kd)r^k from k=0 to ∞ equals a/(1−r) + dr/(1−r)² when |r|<1)

jee-mainjee-advanced

Sum of (a+kd)r^k from k=0 to ∞ equals a/(1−r) + dr/(1−r)² when |r|<1

What each symbol means

SymbolWhat it stands for
rRatio
a,dAP parameters

When to use this

|r|<1 for convergence.