4) VT=n+1n(n+1+n)1=nn+1(n+1−n)n+1−n=nn+1n+1−n=n1−n+11 (đpcm) S=1−21+21−31+.....−1001=1−101=109
5) 1+n21+n+112=n2(n+1)2n2(n+1)2+n2+(n+1)2=n2(n+1)2(n+1)2−2n(n+1)+n2+n2(n+1)2+2n(n+1) =n2(n+1)2(n+1−n)2+2n(n+1)+(n+1)2.n2=n2.(n+1)2(n(n+1)+1)2
Tới đây khai căn là xong
4) VT=n+1n(n+1+n)1=nn+1(n+1−n)n+1−n=nn+1n+1−n=n1−n+11 (đpcm) S=1−21+21−31+.....−1001=1−101=109
5) 1+n21+n+112=n2(n+1)2n2(n+1)2+n2+(n+1)2=n2(n+1)2(n+1)2−2n(n+1)+n2+n2(n+1)2+2n(n+1) =n2(n+1)2(n+1−n)2+2n(n+1)+(n+1)2.n2=n2.(n+1)2(n(n+1)+1)2
Tới đây khai căn là xong