Toán 1.2+2.3+3.4+……….+15.16 tính nhanh giúp mk với nhanh nha 25/07/2021 By Margaret 1.2+2.3+3.4+……….+15.16 tính nhanh giúp mk với nhanh nha
Đặt A=1.2+2.3+3.4+…+15.16 3A=1.2.[3-0]+2.3[4-1]+3.4.[5-2]+….+15.16.[17-14] 3A=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+…+15.16.17-14.15.16 3A=15.16.17 A=5.16.17 A=1360 Trả lời
`A= 1.2+2.3+3,4+….+15.16` `<=> 3.A= 1.2.3 + 2.3.3+….+ 3.15.16` `<=> 3.A= 1.2 . ( 3- 0) + 2.3 . ( 4-1) +…+ 15.16 ( 17- 14)` `<=> 3.A= 1.2.3 + 2.3.4 – 1.2.3 +….+ 15.16.17-14.15.16` `<=> 3.A= 15. 16. 17` `<=> A=1360` Trả lời
Đặt A=1.2+2.3+3.4+…+15.16
3A=1.2.[3-0]+2.3[4-1]+3.4.[5-2]+….+15.16.[17-14]
3A=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+…+15.16.17-14.15.16
3A=15.16.17
A=5.16.17
A=1360
`A= 1.2+2.3+3,4+….+15.16`
`<=> 3.A= 1.2.3 + 2.3.3+….+ 3.15.16`
`<=> 3.A= 1.2 . ( 3- 0) + 2.3 . ( 4-1) +…+ 15.16 ( 17- 14)`
`<=> 3.A= 1.2.3 + 2.3.4 – 1.2.3 +….+ 15.16.17-14.15.16`
`<=> 3.A= 15. 16. 17`
`<=> A=1360`