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Ta có:
\(\frac{945x239-1}{944+945x238}=\frac{945.\left(238+1\right)-1}{944+945x238}\)
\(=\frac{945x238+945-1}{944+945x238}\)
\(=\frac{945x238+944}{944+945x238}=1\)
\(\frac{945x239-1}{944+945x238}\)
=\(\frac{945x\left(238+1\right)-1}{944+945x238}\)
=\(\frac{\left(945x238\right)945-1}{944+945x238}\)
=\(\frac{\left(945x238\right)+944}{944+945x238}\)=1
\(=\frac{945.\left(328+1\right)-1}{\left(945-1\right)+945.328}\)
\(=\frac{945.328+\left(945-1\right)}{\left(945-1\right)+945.328}=1\)
=13/12x14/13x15/14x16/15x...x2006/2005x2007/2006x2008/2007
=2008/12
=502/3
A = 1\(\dfrac{1}{12}\) \(\times\) 1\(\dfrac{1}{13}\) \(\times\) 1\(\dfrac{1}{14}\) \(\times\) 1\(\dfrac{1}{15}\) \(\times\) ... \(\times\) 1\(\dfrac{1}{2005}\) \(\times\) 1\(\dfrac{1}{2006}\) \(\times\) 1\(\dfrac{1}{2007}\)
A = ( 1 + \(\dfrac{1}{12}\)) \(\times\) ( 1 + \(\dfrac{1}{13}\)) \(\times\) ( 1 + \(\dfrac{1}{14}\)) \(\times\)...\(\times\) ( 1 + \(\dfrac{1}{2006}\))\(\times\)(1+\(\dfrac{1}{2007}\))
A = \(\dfrac{13}{12}\) \(\times\) \(\dfrac{14}{13}\) \(\times\) \(\dfrac{15}{14}\) \(\times\) ...\(\times\) \(\dfrac{2007}{2006}\) \(\times\) \(\dfrac{2008}{2007}\)
A = \(\dfrac{13\times14\times15\times...\times2007}{13\times14\times15\times...\times2007}\) \(\times\) \(\dfrac{2008}{12}\)
A = 1 \(\times\) \(\dfrac{502}{3}\)
A = \(\dfrac{502}{3}\)
=1
\(=\dfrac{945\cdot238+945-1}{945-1+945\cdot328}=1\)