1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50＝多少,
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1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50＝多少,1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+4
1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50＝多少,
1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50＝多少,
1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50＝多少,
1/n+2/n+.+(n-1)/n=[1+2+.+n-1]/n={(1+n-1)*(n-1)/2}/n=(n-1)/2
n=2,3,4,.,50
1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+…+1/50+2/50…+49/50
=(2-1)/2+(3-1)/2+.+(50-1)/2
=(2+3+.+50-49)/2
=[(2+50)*49/2-49]/2
=25*49/2
=1225/2
=612.5
=1/2+2/2+3/2+4/2+.......+49/2 的一个等差数列 所以Sn=49*25=1225