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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 6: Bài 1: A = 3/5.8 + 11/8.19 + 12/19.31 + 70/31.101 + 99/101.200 Bài 2: 1/1^2 + 1/2^2 + 1/3^2 + … + 1/n^2 < 2

Home/ Toán Lớp 6: Bài 1: A = 3/5.8 + 11/8.19 + 12/19.31 + 70/31.101 + 99/101.200 Bài 2: 1/1^2 + 1/2^2 + 1/3^2 + … + 1/n^2 < 2

Toán Lớp 6: Bài 1: A = 3/5.8 + 11/8.19 + 12/19.31 + 70/31.101 + 99/101.200 Bài 2: 1/1^2 + 1/2^2 + 1/3^2 + … + 1/n^2 < 2

Tháng Chín 26, 2022 Toán học 1 Comment 0 views

Toán Lớp 6: Bài 1:
A = 3/5.8 + 11/8.19 + 12/19.31 + 70/31.101 + 99/101.200
Bài 2:
1/1^2 + 1/2^2 + 1/3^2 + … + 1/n^2 < 2

Comments ( 1 )

  1. danvanthu
    danvanthu
    26 Tháng Chín, 2022 at 6:27 chiều
    Reply
    1)A = 3/(5.8) + 11/(8.19) + 12/(19.31) + 70/(31.101) + 99/(101.200)
    A=1/5-1/8+1/8-1/19+1/19-1/31+1/31-1/101+1/101-1/200
    A=1/5-1/200
    A=39/200
    2) Đặt A
    Ta có :
    $\dfrac{1}{2^2}< \dfrac{1}{1.2};\dfrac{1}{3^2}< \dfrac{1}{2.3};\dfrac{1}{4^2}< \dfrac{1}{3.4};…;\dfrac{1}{n^2}< \dfrac{1}{\left(n-1\right).n}$
    $\Rightarrow A=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+…+\dfrac{1}{n^2}< \dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+…+\dfrac{1}{\left(n-1\right).n}$
    $\Rightarrow A< 1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+…+\dfrac{1}{n-1}-\dfrac{1}{n}$
    $\Rightarrow A< 1-\dfrac{1}{n}< 1$
    Vậy $A=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+…+\dfrac{1}{n^2}< 1$
     

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222-9+11+12:2*14+14 = ? ( )

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