Đáp án:
`a)``C=2013/3`
`b)``x=(-1)/12`
Giải thích các bước giải:
`a)``C=(1+2/3).(1+2/5).(1+2/7). \ ... \ .(1+2/2009).(1+2/2011)`
`C=5/3*7/5*9/7*...*2011/2009*2013/2011`
`C=(5.7.9. \ ... \ .2011.2013)/(3.5.7. \ ... \ .2009.2011`
`C=2013/3`
`b)``1/2 .x+2/3=5/8-x`
`x/2+3/4=5/8-x`
`x/2+x=5/8-3/4`
`x/2+(2x)/2=(-1)/8`
`(3x)/2=(-1)/8`
`3x=(2(-1))/8`
`3x=(-1)/4`
`x=(-1)/12`