toán khó ai biết giúp giùm

H

hiensau99

Ta có:
[TEX]8A-B= \frac{8}{2}+ \frac{8}{3}+ \frac{8}{4}+ \frac{8}{5}+ \frac{8}{6}+ \frac{8}{7}+ \frac{8}{8}- \frac{1}{7}- \frac{2}{6}- \frac{3}{5}- \frac{4}{4}- \frac{5}{3}- \frac{6}{2} - \frac{7}{1}[/TEX]
[TEX]= (\frac{8}{2}- \frac{6}{2})+(\frac{8}{3}- \frac{5}{3})+(\frac{8}{4}- \frac{4}{4})+(\frac{8}{5}- \frac{3}{5})+(\frac{8}{6}- \frac{2}{6})+(\frac{8}{7}- \frac{1}{7})+1- 7[/TEX]
[TEX]=1.7-7=0[/TEX]
[TEX]=> 8A=B[/TEX] (đpcm)


 
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