If the 2nd and 3rd terms in the expansion of (1+x)nare 20a and 180a2 respectively, then (x,n)=

2nd  term of (1+x)n is C1   nx,3rd  term of (1+x)n is C2   nx2 Given C1   nx=20a and C2   nx2=180a2 ⇒nx=20a→ (1)and n(n-1)2x2=180a2→(2) By (1) and (2) n2x2nn-12x2=400a2180a2⇒2nn-1=209⇒n=10Also (1) ⇒10x=20a⇒x=2a