Ta thấy tổng trên có 50 số hạng .
Ta có:
1/101>1/150
1/102>1/150
...
1/149>1/150
1/150=1/150
=>1/101+1/102+...+1/149+1/150>1/150+1/150+...+1/150
---50 số hạng 1/150-------
=>1/101+1/102+...+1/149+1/150>1/150.50
=>1/101+1/102+...+1/149+1/150>50/150
=>1/101+1/102+...+1/149+1/150>1/3
cho : A= 1/101+1/102+1/103.....+ 1/150
CMR 1/3<a<1/2
cho A=1/101+1/102+1/103+...+1/200 Chứng minh rằng A > 5/8
Chứng minh: \(1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{199}-\frac{1}{200}=\frac{1}{101}+\frac{1}{102}+\frac{1}{103}+...+\frac{1}{199}+\frac{1}{200}\)
Cho A=1/101+1/102+1/103+...+1/200
Chứng minh A>7/12
chứng minh:
A={1/101+1/102+1/103.....................+1/199+1/200
Cho \(S=\frac{1}{101}+\frac{1}{102}+\frac{1}{103}+...+\frac{1}{130}\). Chứng minh 1/4 < S <91/330
cho A=1/101+1/102+1/103+...+1/199+1/200 cmr 5/8<a<3/4
Chứng minh B=1/101+/102+1/103+......+1/199+1/200>7/12
A= \(\frac{1}{101}\)+\(\frac{1}{102}\)+\(\frac{1}{103}\)+...+\(\frac{1}{150}\)
chứng minh rằng \(\frac{1}{3}\)<A<\(\frac{1}{2}\)