`#thanhan12345`
`1+2+3+5+8+...+233`
`\text{Ta thấy : }`
` 1 + 2 = 3`
` 2 + 3 = 5`
` 3 + 5 = 8`
`\text{Tương tự :}`
` 5 + 8 = 13`
` 8 + 13 = 21`
` 13 + 21 = 34`
` 21 + 34 = 55`
` 34 + 55 = 89`
` 55 + 89 = 144`
` 89 + 144 = 233`
`\text{Vậy ta có dãy số: 1 ; 2 ; 3 ; 5 ; 8 ; 13 ; 21 ; 34 ; 55 ; 89 ; 144 ; 233}`
`\text{Tổng : 1 + 2 + 3 + 5 + 8 + 13 + 21 + 34 + 55 + 89 + 144 + 233}`
` = ( 1 + 2 ) + 3 + ( 5 + 8 ) + 13 + ( 21 + 34 ) + 55 + ( 89 + 144 ) + 233`
` = 3 + 3 + 13 + 13 + 55 + 55 + 233 + 233`
` = 2 . ( 3 + 13 + 55 + 233 )`
` = 2 . 304`
` = 608`
