Chứng minh bằng quy nạp: a/$1^3+2^3+3^3+.....n^3=(1+2+3+...+n)^2$ b/1.2+2.3+3.4+4.5+....+n(n+1)=$/dfrac{n(n+1)(n+2)}{3}$ c/$1^2+2^2+3^2+...+n^2$=$/dfrac{n(n+1)(2n+1)}{6}$ d/1.n+2(n−1)+3(n−2)+.....+n.1=$\dfrac{n(n+1)(n+2)}{6}$ | ||
Chứng minh bằng quy nạp: a/$1^3+2^3+3^3+.....n^3=(1+2+3+...+n)^2$ b/1.2+2.3+3.4+4.5+....+n(n+1)=$/dfrac{n(n+1)(n+2)}{3}$ c/$1^2+2^2+3^2+...+n^2$=$/dfrac{n(n+1)(2n+1)}{6}$ d/1.n+2(n−1)+3(n−2)+.....+n.1=$\dfrac{n(n+1)(n+2)}{6}$ | ||
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