To create cheat sheet first you need to select formulas which you want to include in it. To select formula click at picture next to formula.
You can choose formulas from different pages.
After you have selected all the formulas which you would like to include in cheat sheet, click the "Generate PDF" button.
Number of terms in the series: $n$
First term: $a_1$
$N^{th}$ term: $a_n$
Sum of the first $n$ terms: $S_n$
Difference between successive terms: $d$
Common ratio: $q$
Sum to infinity: $S$

$$ a_n = a_1 + (n1)d $$ 

$$ a_i = \frac{a_{i1} + a_{i+1}}{2} $$ 

$$ S_n = \frac{a_1 + a_n}{2} \cdot n $$ 

$$ S_n = \frac{2 \cdot a_1 + (n1) \cdot d}{2} \cdot n $$ 

$$ a_n = a_1 \cdot q^{n1} $$ 

$$ a_i = \sqrt{a_{i1} \cdot a_{i+1}} $$ 

$$ S_n = \frac{a_nq  a_1}{q1} $$ 

$$ S_n = \frac{a_1 \cdot \left(q^n  1 \right)}{q1} $$ 

$$ S = \frac{a_1}{1q}, \quad (\text{for } 1 < q < 1)$$ 
Please tell me how can I make this better.