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3n/3x 2n+3 =n/2n+1
n/2n+1=3n/3x2n+3=3n/6n+3<3n/6n+2
n/2n+1<3n+1/6n+2
Ta có: \(\frac{n}{n+1}=\frac{n\times n+2}{n+1\times n+2}\)
\(\frac{n+1}{n+2}=\frac{n+1\times n+1}{n+2\times n+1}=\frac{n\times2}{n\times3}\)
=> n + 1/ n + 2 > n/n+1
có Q=3n+1/6n+3
=3n/(6n+3)+1/(6n+3)
=3n/3.(2n+1)+1/6n+3
=n/3n+1+1/6n+3
Ta có :
A = n / 2n + 1 = 3n / 3 ( 2n + 1 ) = 3n / 6n + 3
Vì 3n / 6n + 3 < 3n + 1/ 6n + 3 => A < B
Vậy A < B
\(\frac{n}{2n+1}\)=\(\frac{3.n}{3.\left(2n+1\right)}\)=\(\frac{3n}{6n+3}\)
Vì 6n+3=6n+3;3n<3n+1 nên \(\frac{n}{2n+1}\)<\(\frac{3n+1}{6n+3}\)
\(A=\dfrac{n}{2n+1}=\dfrac{n\left(6n+3\right)}{\left(2n+1\right)\left(6n+3\right)}\dfrac{6n^2+3n}{\left(2n+1\right)\left(6n+3\right)}\)
\(B=\dfrac{3n+1}{6n+3}=\dfrac{\left(3n+1\right)\left(2n+1\right)}{\left(6n+3\right)\left(2n+1\right)}=\dfrac{6n^2+5n+1}{\left(6n+3\right)\left(2n+1\right)}\)
Lại có :
\(6n^2+3n< 6n^2+5n+1\)
\(\Leftrightarrow A< B\)
A=n2n+1=n(6n+3)(2n+1)(6n+3)6n2+3n(2n+1)(6n+3)
B=3n+16n+3=(3n+1)(2n+1)(6n+3)(2n+1)=6n2+5n+1(6n+3)(2n+1)
Lại có :
6n2+3n<6n2+5n+1
Ta có: \(\frac{n}{2n+1}=\frac{3n}{6n+3}\)
Vì 3n < 3n + 1 nên \(\frac{3n}{6n+3}<\frac{3n+1}{6n+3}\)
Vậy \(\frac{n}{2n+1}<\frac{3n+1}{6n+3}\)
Ta có:
n/2n + 1 = 3n/6n + 3
3n/6n + 3 < 3n + 1/6n + 3
=>n/2n + 1 <3n + 1/6n + 3
Thanks!