Question

[Nguyễn Xuân Thủy]

Cho A =1/3mũ 2 +1/4mũ 1+1/5 mũ 1+1/6mux 1+1/7mũ 1+1/8 mũ 2 .Chứng minh 2/9<A<3/8

Nhanh dùm nha tick cho thank u rất nhìu dùm nha các bạn chú ý cách giả nữa nha

Answer 1

[Vũ Minh DŨng]

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2 > 1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2  > 1/3- 1/4+1/4-1/5+1/501/6+1/6-1/7+1/7-1/8+1/8-1/9

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2  > 3/9-1/9

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2  > 2/9

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2  < 1/2.3 +1/3.4+1/4.5+1/5.6+1/6.7+1/7.8

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2 < 1/2 -1/3+1/3-1/4+1/4-1/5+1/6-1/7+1/7-1/8

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2 < 1/2-1/8

1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2  < 3/8 vậy ta có 2/9< 1/3^2+1/4^2+1/5^2+1/6^2 +1/7^2 1/8^2 <3/8

Answer 2

[Nguyễn Xuân Thủy]

thank u bạn Vũ Minh DŨng nhìu nha mình tịk cho pạn zồi ak nha