tính tổng sau :3/1×2+7/2×3+13/3×4+21/4×5+31/5×6+43/6×7.help mik nha 10/09/2021 Bởi Kennedy tính tổng sau :3/1×2+7/2×3+13/3×4+21/4×5+31/5×6+43/6×7.help mik nha
`3/(1times2)+7/(2xx3)+13/(3xx4)+21/(4xx5)+31/(5xx6)+43/(6xx7)` `=(1/(1times2)+1)+(1/(2xx3)+1)+(1/(3xx4)+1)+(1/(4xx5)+1)+(1/(5xx6)+1)+(1/(6xx7)+1)` `=(1/(1times2)+1/(2xx3)+1/(3xx4)+1/(4xx5)+1/(5xx6)+1/(6xx7))+(1+1+1+1+1+1)` `=(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)+6` `=1-1/7+6` `=48/7` Bình luận
3/1×2+7/2×3+13/3×4+21/4×5+31/5×6+43/6×7. = 1/1.2+ 2/1.2+ 1/2.3+ 6/2.3+ 1/3.4+ 12/3.4+ 1/4.5+ 20/4.5+ 1/5.6+ 30/5.6+ 1/6.7+ 42/6.7 = ( 1/1.2+ 1/2.3+ 1/3.4+….+ 1/6.7)+ ( 2/2+ 6/6+ 12/12+ 20/20+ 30/30+ 42/42) = ( 1- 1/2+ 1/2- 1/3+..+ 1/6- 1/7)+( 1+ 1+ 1+ 1+1+1) =( 1- 1/7)+ 6 = 6/7+ 6 = 48/7 Chúc em học tốt! Bình luận
`3/(1times2)+7/(2xx3)+13/(3xx4)+21/(4xx5)+31/(5xx6)+43/(6xx7)`
`=(1/(1times2)+1)+(1/(2xx3)+1)+(1/(3xx4)+1)+(1/(4xx5)+1)+(1/(5xx6)+1)+(1/(6xx7)+1)`
`=(1/(1times2)+1/(2xx3)+1/(3xx4)+1/(4xx5)+1/(5xx6)+1/(6xx7))+(1+1+1+1+1+1)`
`=(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)+6`
`=1-1/7+6`
`=48/7`
3/1×2+7/2×3+13/3×4+21/4×5+31/5×6+43/6×7.
= 1/1.2+ 2/1.2+ 1/2.3+ 6/2.3+ 1/3.4+ 12/3.4+ 1/4.5+ 20/4.5+ 1/5.6+ 30/5.6+ 1/6.7+ 42/6.7
= ( 1/1.2+ 1/2.3+ 1/3.4+….+ 1/6.7)+ ( 2/2+ 6/6+ 12/12+ 20/20+ 30/30+ 42/42)
= ( 1- 1/2+ 1/2- 1/3+..+ 1/6- 1/7)+( 1+ 1+ 1+ 1+1+1)
=( 1- 1/7)+ 6
= 6/7+ 6
= 48/7
Chúc em học tốt!