Sửa đề:1/1*3+2/3*7+3/7*13+4/13*21+5/21*31
=1/2(2/1*3+4/3*7+6/7*13+8/13*21+10/21*31)
=1/2(1-1/3+1/3-1/7+...+1/21-1/31)
=1/2*30/31=15/31
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Các câu hỏi tương tự
A = 1/1.3 + 2/3.7 + 3/7.13 + ... +10/91.111
Tính nhanh :
-13.21-13.80+13
-1+2-3+4-5+6-...-2021+2022
1. tính:
a) 1.3+2.4+3.5+4.6+...+n.(n+2)
b) 1.5+2.6+3.7+...+n.(n+4)
c) 12 + 32+52+...+(2n+1)2
Tính:
a) C = 3/1.3 + 3/3.5 + 3/3.7 +...+ 3/49.51
b) D = 1/2 + 1/14 + 1/35 + 1/65 + 1/104 + 1/152
20 tháng 3 2023 lúc 23:25
A=2/1.3+2/3.5+2/3.7+....+2/2021.2023
=)
B=1/2.5+1/5.8+1/8.11+...+1/95.98
Tính 1/1.3+1/3.5+1/3.7+.......+1/101.103
Tính 1/1.3+1/3.5+1/3.7+........+1/101.103
chứng tỏ A =\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{3.7}+...+\frac{2}{99.101}\) >1
B= 6/1.3+6/3.5+6/3.7+......+6/97.99
C=1/2 + 1/6 + 1/12 + 1/ 20 + 1/30 + 1/42
D= 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128
Giúp mik vs nha mn ^^