Question

[Tạ Ngọc Khuê]

1/1.7+1/7.13+1/13.19+......+1/61.67

1/1.2.3+1/2.3.4+1/3.4.5+.......+1/8.9.10

1/1+2 + 1/1+2+3 + 1/1+2+3+4 +.......+ 1/1+2+3+....+99

CẦN GẤP

Answer 1

[no name 2k7]

\(\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+...+\frac{1}{61.67}\)

=6.\(\left(\frac{1}{1.7}+\frac{1}{7.13}+...+\frac{1}{61.67}\right)\):6

=\((\frac{6}{1.7}+\frac{6}{7.13}+...+\frac{6}{61.67}):6\)

=\(\left(1-\frac{1}{7}+\frac{1}{7}+\frac{1}{13}+...+\frac{1}{61}+\frac{1}{67}\right):6\)

=\(\left(1-\frac{1}{67}\right):6\)

=\(\frac{66}{67}:6=\frac{66}{67}.\frac{1}{6}=\frac{11}{67}\)