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1/302 < 1/301; 1/303<1/301; ...; 1/400<1/301

=> A < 1/2 + 1/301+1/301+...+1/301=1/2 + 100/301< 1/2+100/300=1/2+1/3=5/6<1

=> A<1 => đpcm

A=1/2+1/301+1/302+1/303+.....+1/399+1/400

Có:1/100>1/301

     1/200>1/302

     1/200>1/303

     .........

   1/200>1/399

  1/200>1/400

<=>1/2+1/301+1/302+1/303+...+1/399+1/400<1/2+1/200+1/200+...+1/200+1/200(100 chữ số 1/200)

<=>A<1/2+100/200

<=>A<1

Vậy A<1

\(A=\dfrac{1}{2}+\dfrac{1}{301}+\dfrac{1}{302}+...+\dfrac{1}{400}\)

Do \(\dfrac{1}{301}< \dfrac{1}{300};\dfrac{1}{302}< \dfrac{1}{300};...;\dfrac{1}{400}< \dfrac{1}{300}\)

\(\Rightarrow A< \dfrac{1}{2}+\dfrac{1}{300}+\dfrac{1}{300}+...+\dfrac{1}{300}+\dfrac{1}{300}\) (100 số \(\dfrac{1}{300}\) )

\(\Rightarrow A< \dfrac{1}{2}+\dfrac{100}{300}\)

\(\Rightarrow A< \dfrac{1}{2}+\dfrac{1}{3}=\dfrac{5}{6}< 1\)

Vậy \(A< 1\)

1/1x300+1/2x301+1/302+304+1/101x400=con cặc

Đặt B=1/301+1/302+...+1/399+1/400.

Để só sánh A với 1 ta cần so sánh B với 2.

Số số hạng của B là:

(400-301):1+1=100(số hạng).

Vì 1/301<1/300;

1/302<1/300.

.....

1/399<1/300.

1/400<1/300.

=>B<1/300*100.

=>B<1/3.

=>A<1/2+1/3=5/6<1.

Vậy A<1.

giúp mk với mn huhu

Cho A = 1-4-7+10+13-16-19+22+....-295+298+301-304.Chứng minh rằng A:3