sequences & series formulae

overall Un equation

overall Un equation

Un = Sn - Sn-1

common difference of AP

Un - Un-1 = d

Un of AP

Un = a + (n-1)d

Sn of AP

Sn = (n/2)[2a + (n-1)d] OR Sn = (n/2)(a + l)

Common ratio of GP

Un/Un-1 = r

Un of GP

Un = ar^(n-1)

Sn of GP

Sn = a(1-r^n)/(1-r) OR Sn = a(r^n-1)/r-1

condition for sum to infinity for GP

|r| < 1

Sum to infinity for GP

Sum to infinity = a/(1-r)