A = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 +1/72 + 1/90
A = 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 + 1/9.10
A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 +1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 + 1/9 -1/10
A = 1/1 - 1/10
A = 10/10 - 1/10
A = 9/10
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