AP, GP and HP
Posted March 25, 2009on:
Example: a, a+d, a+2d…..where ‘a’ is the first term and ‘d’ is the common difference.
Nth Term: a + (n-1)d
Sum to N terms : n/2 [2a + (n-1+d] or n/2[First Term + Last Term]
AP of 3 terms: a-d, a, a+d
AP of 4 terms: a-3d, a-d, a+d, a+3
Example: a, ar, ar^2, ar^3….. where ‘a’ is the first term and ‘r’ is the common ratio
Nth Term: ar^(n-1)
Sum to N terms: [a((r^n) – 1)/r-1], signs change if r < 1.
Sum to Infinity: a/(1-r), if r<1
3 terms of a GP: a/r, a, ar
4 terms of a GP: a/r^3, a/r, ar, ar^3