Đáp án:
Giải thích các bước giải:
B=3/3+3/15+3/35+3/63+3/99+3/143
B= 1 + 3/15+3/35+3/63+3/99+3/143
Đặt A = 3/15+3/35+3/63+3/99+3/143
B = 1
A = 5. (3/15+3/35+3/63+3/99+3/143)
A = 5/2. (2/15+2/35+2/63+2/99+2/143)
A = 5/2. ( 2/3,5+2/5,7+2/7,9+2/9,11+2/11,13)
A = 5/2. ( 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13)
A = 5/2. ( 1/3 - 1/13)
A = 5/2.10/39
A = 50/78 = 25/39
Ta có :
= 1 + 25/39 = 39/39 + 25/39 = 64/39
Vậy B = 64/39