a) Gọi d là UCLN(n+1;2n+3)
\(n+1⋮d\Rightarrow2\left(n+1\right)⋮d\Rightarrow2n+2⋮d\)
\(2n+3⋮d\)
\(\Leftrightarrow\left(2n+3\right)-\left(2n+2\right)⋮d\)
\(2n+3-2n-2⋮d\)
\(1⋮d\)
\(\dfrac{n+1}{2n+3}\)tối giản
b) Gọi d là UCLN(2n+1;4n+1)
\(2n+1⋮d\Rightarrow2\left(2n+1\right)⋮d\Rightarrow4n+2⋮d\)
\(4n+1⋮d\)
\(\Leftrightarrow\left(4n+2\right)-\left(4n+1\right)⋮d\)
\(4n+2-4n-1⋮d\)
\(1⋮d\)
\(\Leftrightarrow\dfrac{2n+1}{4n+1}\)tối giản
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