Tính `A=12/(5.2.5)+12/(5.5.8)+...+12/(5.17.20)`.

Question

haiyen · Answer

Đ&aacute;p &aacute;n:       Giải th&iacute;ch c&aacute;c bước giải:    Ta c&oacute; :A=12/5.2.5+12/5.5.8+. . .+12/5.17.20               A =`1/5` x `12/2.5`+`1/5` x `12/5.8`+. . .+`1/5` x `12/17.20`              A = `1/5` x(`12/2.5`+`12/5.8`+. . .+`12/17.20` )              A = `1/5` x 4 x(`3/2.5`+`3/5.8`+. . .+`3/17.20`)              A = `4/5` x ( `1/2`-`1/5`+`1/5`-`1/8`+. . .+`1/17`-`1/20`)              A = `4/5` x ( `1/2`-`1/20`)              A = `4/5` x `9/20`              A =`9/25`

aivilan · Answer

Đ&aacute;p &aacute;n+Giải th&iacute;ch c&aacute;c bước giải:    `A=12/(5.2.5)+12/(5.5.8)+...+12/(5.17.20)`   `=4.3/(5.2.5)+4.3/(5.5.8)+...+4.3/(5.17.20)`   `=4/(5).(3/2.5+3/5.8+...+3/17.20)`   `=4/(5).(1/2-1/5+1/5-1/8+...+1/17-1/20)`   `=4/(5).(1/2-1/20)`   `=4/(5).(10/20-1/20)`   `=4/(5).(9)/20`   `=9/25`   Vậy `A=9/25`

Tính `A=12/(5.2.5)+12/(5.5.8)+…+12/(5.17.20)`.

Viết một bình luận Hủy