Toán Lớp 5: S = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
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Toán Lớp 5: S = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
Comments ( 2 )
⇒ S = 1/(1.2) + 1/(2.3) + 1/(3.4) + 1/(4.5) + 1/(5.6) + 1/(6.7) + 1/(7.8)
⇒ S = 1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + … + 1/7 – 1/8
⇒ S = 1 – 1/8
⇒ S = 8/8 -1/8
⇒ S = 7/8