= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6
= ( 1 - 1/2 ) + ( 1/2 - 1/3 ) + ( 1/3 - 1/4 ) + ( 1/4 - 1/5 ) + ( 1/5 - 1/6 )
= 1 -1/6
= 5/6
= 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + 1/5* 6
= 1- 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6
= 1- 1/6
= 5/6
1/2 + 1/6 + 1/12 + 1/20 + 1/30
= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6
= ( 1 - 1/2 ) + ( 1/2 - 1/3 ) + ( 1/3 - 1/4 ) + ( 1/4 - 1/5 ) + ( 1/5 - 1/6 )
= 1 -1/6
= 5/6
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\)
=\(\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}\right)+\left(\frac{1}{20}+\frac{1}{30}\right)\)
=\(\left(\frac{6}{12}+\frac{2}{12}+\frac{1}{12}\right)+\left(\frac{3}{60}+\frac{2}{60}\right)\)
=\(\frac{9}{12}+\frac{1}{12}\)
=\(\frac{5}{6}\)
k cho mk nhé...
= [ 1/2+1/12]+[1/6+1/30]+1/20
=7/12+1/5=47/60+1/20
=50
