rất đơn giản
nhân 3 vào tư và mẫu sau đó tách \(\frac{1}{3}\) ra
ta có \(\frac{1}{3}.\left(\frac{6}{1.7}+\frac{6}{7.13}+...+\frac{6}{601.607}\right)\)
=\(\frac{1}{3}.\left(\frac{1}{1}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{601}-\frac{1}{607}\right)\)
=1/3 . ( 1-1/207)
bây giờ tự tính nha
\(2\left(\frac{1}{1.7}+\frac{1}{7.13}+...+\frac{1}{601.607}\right)\)
\(2.\frac{1}{6}\left(\frac{1}{1}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{601}-\frac{1}{607}\right)\)
\(\frac{1}{3}\left(\frac{1}{1}-\frac{1}{607}\right)\)
\(\frac{1}{3}.\frac{606}{607}=\frac{202}{607}\)
A= ( \(\frac{2}{1x7}+\frac{2}{7x13}+\frac{2}{13x19}\) \(+...+\frac{2}{601x607}\) ) x 3 : 3
A= ( \(\frac{6}{1x7}+\frac{6}{7x13}+\frac{6}{13x19}\) \(+...+\frac{6}{601x607}\) ) :3
A=( 1 - \(\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}\) \(-\frac{1}{19}+...+\frac{1}{601}\) \(-\frac{1}{607}\) ) : 3
A= ( 1\(-\frac{1}{607}\) ) : 3
A = \(\frac{606}{607}\) :3
A= \(\frac{606}{1221}\)
\(A=\frac{1}{3}.\left(\frac{2}{1.7}+\frac{2}{7.13}+\frac{2}{13.19}+...+\frac{2}{601.607}\right)\)
\(A=\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+...+\frac{6}{601.607}\)
\(A=\frac{1}{1}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{601}-\frac{1}{607}\)
\(A=\frac{1}{1}-\frac{1}{607}\)
\(A=\frac{606}{607}\)
2(11.7+17.13+...+1601.607)2(11.7+17.13+...+1601.607)
2.16(11−17+17−113+...+1601−1607)2.16(11−17+17−113+...+1601−1607)
13(11−1607)13(11−1607)
13.606607=202607
