Tính tổng sau 1/3+1/5.7+1/7.9+...+1/999.1001
2 câu trả lời
13+15.7+17.9+...+1999.1001
=13+(15.7+17.9+...+1999.1001)
=13+12(15-17+17-19+...+1999-11001)
=1/3+1/2(1/5 - 1/1001)
= 1/3+1/2 . 996/5005
= 1/3+498/5005
= 6499/15015
1/3 + 1/(5.7) + 1/(7.9) + ... + 1/(999.1001)
= 1/3 + (1/(5.7) + 1/(7.9) + ... + 1/(999.1001))
= 1/3 + 1/2 . (2/(5.7) + 2/(7.9) + ... + 2/(999.1001) )
= 1/3 + 1/2 . (1/5 - 1/7 + 1/7 - 1/9 + ... + 1/999 - 1/1001)
= 1/3 + 1/2 . (1/5 - 1/1001)
= 1/3 + 1/2 . 996/5005
= 1/3 + 498/5005
= 6499/15015
