lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2)]}=()?3/4

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lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2)]}=()?3/4lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2

lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2)]}=()?3/4
lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2)]}=()?
3/4

lim{[1/(1*3)]+[1/(2*4)]+[1/(3*5)]+……+[1/n(n+2)]}=()?3/4
1/n(n+2) = (1/n - 1/n+2) / 2
原式=
limit 1/2 * (1/1 - 1/3 + 1/2 - 1/4 + 1/3 - 1/5 + ...+ 1/n-1 - 1/n+1 + 1/n - 1/n-2)
=
limit 1/2 * (1 + 1/2 - 1/n-1 - 1/n)
=
limit 1/2 * 3/2= 3/4