=1/11-1/13+1/13-1/15+1/15-..................+1/99-1/100
=1/11 -1/100
=89/1100
=1/11-1/13+1/13-1/15+1/15-..................+1/99-1/100
=1/11 -1/100
=89/1100
2/11*13+2/13*15+15*17+.....+2/97*99+2/99*101
giup minh voi minh can gap ai dung minh tick cho
a.1/6+1/12+1/20+1/30+1/42+............+1/90+1/110
b.2/11*13+2/13*15+2/15*17+..........+2/97*99+2/99*101
c.1/11*16+1/16*21+1/21*26+.................+1/56*61+1/61*66
tính nhanh tổng sau :
1-3+5-7+9-11+13-15+17-19+...+97-99+101
2/11*13+2/13*15+2/15*17+2/17*19+2/19*21
tính thuận tiện
a ( 145 * 99 - 145 ) - ( 143 * 101 - 143 )
b ( 500 * 9 - 250 * 18 ) * ( 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 +9 )
c ( 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 ) * ( 6 * 8 - 48)
(2/11*13+2/13*15+2/15*17+2/17*19+2/19*21)*462-y=19
(2/11×13+2/13×15+2/15×17+2/17×19+2/19×21)×462-x=19
2/(11*13)+2/(13*15)+2/(15*17)+2/(17*19)+2/(19*21)*462-y=19
tính nhanh tổng sau :
1-3+5-7+9-11+13-15+17-19..........+97-99+101