Question

Sa se calculeze suma ( probleme de numărare )​

Answer 1

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Answer 2

a)Sn=1!/3!+2!/4!+3!/5!+...+n!/(n+2)!=

1!/3!+2!/2!3×4+3!/3!×4×5+n!/n!×(n+1)(n+2)=

1/2×3+1/3×4+1/4×5+...+1/(n+1)(n+2)=

1/2-1/3+1/3-1/4+1/5-1/5+...+1/(n+1)-1/(n+2)=

1/2-1/(n+2)=(n+2-1)/(n+2)=(n+1)/(n+2)