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A = 1/90 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
A = 1/90 - ( 1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)
A = 1/90 - ( 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72)
A = 1/90 - ( 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9)
A = 1/90 - ( 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9)
A = 1/90 - ( 1 - 1/9)
A = 1/90 - 8/9
A = 1/90 - 80/90 = -79/90
A=1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
A=1/90-(1/72+1/56+1/42+1/30+1/20+1/12+1/6+1/2)
A=1/90-(1-1/9)
A=1/90-8/9=1/90-80/90=-79/90
A = 1/90 - ( 1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)
A = 1/90 - ( 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72)
A = 1/90 - ( 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9)
A = 1/90 - ( 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9)
A = 1/90 - ( 1 - 1/9)
A = 1/90 - 8/9
A = 1/90 - 80/90 = -79/90
A = 1/90 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
A = 1/90 - ( 1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)
A = 1/90 - ( 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72)
A = 1/90 - ( 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9)
A = 1/90 - ( 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9)
A = 1/90 - ( 1 - 1/9)
A = 1/90 - 8/9
A = 1/90 - 80/90 = -79/90
Câu trả lời của soyeon và tuổi trer tài cao là chính xác