Question

[Nam Joo Hyuk]

So sánh A và B biết:

a) A= \(\dfrac{15^{16}+1}{15^{17}+1}\) và B= \(\dfrac{15^{15}+1}{15^{16}+1}\)

b) A= \(\dfrac{2006^{2007}+1}{2006^{2006}+1}\) và B= \(\dfrac{2006^{2006}+1}{2006^{2005}+1}\)

c) A= \(\dfrac{1000^9+2}{1000^9-1}\) và B= \(\dfrac{1000^9+1}{1000^9-2}\)

Answer 1

[Đậu Thị Khánh Huyền]

a) Vì A=\(\dfrac{15^{16}+1}{15^{17}+1}\) < 1

\(\Rightarrow\dfrac{15^{16}+1}{15^{17}+1}< \dfrac{15^{16}+1+14}{15^{17}+1+14}=\dfrac{15^{16}+15}{15^{17}+15}\) \(=\dfrac{15\left(15^{15}+1\right)}{15\left(15^{16}+1\right)}\) \(=\dfrac{15^{15}+1}{15^{16}+1}\)

Vậy A<B

Answer 2

[Đậu Thị Khánh Huyền]

b) A=\(\dfrac{2006^{2007}+1}{2006^{2006}+1}>1\)

\(\Rightarrow\dfrac{2006^{2007}+1+2005}{2006^{2006}+1+2005}\)

= \(\dfrac{2006^{2007}+2006}{2006^{2006}+2006}\)

= \(\dfrac{2006\left(2006^{2006}+1\right)}{2006\left(2006^{2005}+1\right)}\)

= \(\dfrac{2006^{2006+1}}{2006^{2005}+1}\)

Vậy A>B