Toán Lớp 6: B = 1/3.5 + 1/5.7 + 1/7.9+ 1/9.11 + 1/11.13
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Toán Lớp 6: B = 1/3.5 + 1/5.7 + 1/7.9+ 1/9.11 + 1/11.13
Comments ( 2 )
Giải đáp:
5/39
Lời giải và giải thích chi tiết:
1/(3. 5) + 1/(5. 7) + 1/(7. 9) + 1/(9. 11) + 1/(11 + 13)
= 2/2. (1/(3. 5) + 1/(5. 7) + 1/(7. 9) + 1/(9. 11) + 1/(11 + 13))
= 1/2. (2/(3. 5) + 2/(5. 7) + 2/(7. 9) + 2/(9. 11) + 2/(11 + 13))
= 1/2. (1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13)
= 1/2. (1/3 – 1/13)
= 1/2. 10/39
= 5/39
B=1/3.5+1/5.7+1/7.9+1/9.11+1/11.13
B=1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13
B=(1/5-1/5)+(1/7-1/7)+(1/9-1/9)+(1/11-1/11)+1/3-1/13
B=1/3-1/13
B=13/39-3/39
B=10/39