rev correction

content/ctf-writeups/bcactf_5.0/rev.md

@@ -89,19 +89,21 @@ sum(comb(\{a_1, a_2, a_3\})) = \frac{2a_1a_2 + 2a_2a_3 + 2a_1a_3 + {a_1}^2 + {a_
 $$
 
 $$
-
 sum(comb(\{a_1, a_2, a_3\})) = \frac{(a_1 + a_2 + a_3)^2 - (a_1 + a_2 + a_3)}{2}  
-
 $$
 
+
+
+
 In general:
+
+$$
+sum(comb(\{a_1, a_2, a_3, ...a_n\})) = \frac{\sum{a_i}* (\sum{a_i}-1)}{2}    
 $$
-sum(comb(\{a_1, a_2, a_3, ...a_n\})) = \frac{\sum{a_i}* (\sum{a_i}-1)}{2} 
-$$   
 
-or, 
+or,
 
-$$
+$$ 
 sum(comb(comb(\{a_1, a_2, a_3, ...a_n\}))) = \frac{\sum{a_i} * (\sum{a_i}-1) * (\sum{a_i}-2) * (\sum{a_i}+1)}{8}
 $$