(n+2)!(n+3−1)=42n!(n+1+1)
(n+2)(n+1).n!.(n+2)=42.n!(n+2)
n+2)(n+1)=42
n=5 dir.
(n+3)(n+2)(n+1)n!−(n+2)(n+1)n!=42n![(n+1)+1]
⇒
(n+3)(n+2)(n+1)−(n+2)(n+1)=42[(n+1)+1]
(n+2)(n+1)[(n+3)−1)]=42(n+2)
(n+2)(n+1)=42
n=…