AP GP

AP GP for some reasons seem to pose an unnecessary hurdle to students. Let's wipe off this anomaly! AP GP is hard usually because students:
1) don't bother to memorise the required formula or half-hearted effort
2) can't get past the English while converting the statements into Maths equations

For the 1st hurdle, only you can surpass it. Just do it! Memorise the right formula for the right thing! Make the effort, remember the right stuff.

As for the English part, with enough practice and systematic conversion, taking note of keywords, the second hurdle can also be overcomed.

Formula to remember:

Tn for AP = a + (n - 1)d
Sn for AP = (n/2)(2a + (n - 1)d)

Tn for GP = ar^(n - 1)
Sn for GP = a(1 - r^n)/(1 - r)

Soo exists if and only if /r/ < 1
Soo = a/(1 - r)

For any progression, Tn = Sn - Sn-1
This is true even if it's not an AP or GP.

Based on the characteristics of AP and GP, we also have the following concepts:

To prove that a progression is an AP, show that Tn - Tn-1 = constant (independent of n). This constant is the common difference d of the AP.

To prove that a progression is a GP, show that Tn/Tn-1 = constant (independent of n). This constant is the common ratio r of the GP.

So there you have it, all the concepts involved in Chp 2(r). Master and apply them skillfully, and you are on your way to scoring for AP GP :-)