For some positive integer $n,$ the expansion of $(1 + y)^n$ has three consecutive coefficients $a,$ $b,$ $c$ that satisfy $a:b:c = 1:7:35.$ What must $n$ be?
Pls explain your solution because I don't really understand this type of stuff.
See heureka's excellent solution, here :
https://web2.0calc.com/questions/help_73560#r2
yeah, but I still kind of don't understand it completely.
