Tính tổng: A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90 giúp mình với ạ. Mình đang cần gấp 08/08/2021 Bởi Delilah Tính tổng: A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90 giúp mình với ạ. Mình đang cần gấp
A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90 =1-1/2+1-1/6+1-1/12+1-1/20+1-1/30+1-1/42+1-1/56+1-1/72+1-1/90 =9 – (1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90) =9 – [1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)+1/(9×10)] =9 – ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10) =9 – (1 – 1/10) = 9 – 9/10 = 81/10 Bình luận
Đáp án: `A = 8,1` Giải thích các bước giải: `A = 1/2 + 5/6 + 11/12 + 19/20 + 29/30 + 41/42 + 55/56 + 71/72 + 89/90` `A = (1 – 1/2) + (1 – 1/6) + (1 – 1/12) + (1 – 1/20) + … + (1 – 1/72) + (1 – 1/90)` `A = 1 × 9 – (1/2 + 1/6 + 1/12 + 1/20 + … + 1/90)` `A =` $9 -(\dfrac{1}{1 × 2} + \dfrac{1}{2 × 3} + \dfrac{1}{3 × 4} + … + \dfrac{1}{9 × 10})$ `A = 9 – (1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + … + 1/9 – 1/10)` `A = 9 – (1 – 1/10)` `A = 9 – 9/10` `A = 81/10 = 8,1` Bình luận
A=1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90
=1-1/2+1-1/6+1-1/12+1-1/20+1-1/30+1-1/42+1-1/56+1-1/72+1-1/90
=9 – (1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=9 – [1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)+1/(9×10)]
=9 – ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)
=9 – (1 – 1/10) = 9 – 9/10 = 81/10
Đáp án:
`A = 8,1`
Giải thích các bước giải:
`A = 1/2 + 5/6 + 11/12 + 19/20 + 29/30 + 41/42 + 55/56 + 71/72 + 89/90`
`A = (1 – 1/2) + (1 – 1/6) + (1 – 1/12) + (1 – 1/20) + … + (1 – 1/72) + (1 – 1/90)`
`A = 1 × 9 – (1/2 + 1/6 + 1/12 + 1/20 + … + 1/90)`
`A =` $9 -(\dfrac{1}{1 × 2} + \dfrac{1}{2 × 3} + \dfrac{1}{3 × 4} + … + \dfrac{1}{9 × 10})$
`A = 9 – (1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + … + 1/9 – 1/10)`
`A = 9 – (1 – 1/10)`
`A = 9 – 9/10`
`A = 81/10 = 8,1`