Ta có:
\(S=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+.......+\frac{3}{2015.2016}\)
\(\Rightarrow\frac{1}{3}.S=\frac{1}{1.2}+\frac{1}{2.3}+......+\frac{1}{2015.2016}\)
\(\Rightarrow\frac{1}{3}.S=\left(1-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{3}\right)+......+\left(\frac{1}{2015}-\frac{1}{2016}\right)\)
\(\Rightarrow\frac{1}{3}.S=1-\frac{1}{2016}=\frac{2015}{2016}\)
\(\Rightarrow S=\frac{2015}{672}\)
Vậy: S = 2015/672
hãy xem đây 5'
tôi làm cho chắc chắn bn kia sai
ko cần kb đâu
\(S=\frac{1}{3}\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+........+\frac{1}{2015}-\frac{1}{2016}\right).\)
\(S=\frac{1}{3}\left(1-\frac{1}{2016}\right)=\frac{1}{3}x\frac{2015}{2016}=\frac{2015}{6048}\)
vậy ......
mk làm tắt đó
\(S=3\left(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{2015\times2016}\right)\)
\(S=3\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)
\(S=3\left(1-\frac{1}{2016}\right)\)
\(S=3\times\frac{2015}{2016}\)
\(S=\frac{2015}{672}\)
hùng sai zùi 1/3 chứ ko phải hôm nay tui kiểm tra bài này nè
theo tôi là nguyên làm đúng vì cô giáo cx ns thế
S=\(3\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)
S=\(3\left(1-\frac{1}{2016}\right)\)
S=\(3.\frac{2015}{2016}\)
S=\(\frac{2015}{672}\)
\(S=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2014.2015}+\frac{1}{2015.2016}\right)\)
\(S=3.\left(1-\frac{1}{2016}\right)\)
\(S=3.\frac{2015}{2016}\)
\(S=\frac{2015}{672}\)
Chúc bạn học tốt !!!
\(S=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{2015.2016}\)
\(=3\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2015.2016}\right)\)
\(=3\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)
\(=3\left(1-\frac{1}{2016}\right)\)
\(=3.\frac{2015}{2016}\)
\(=\frac{2015}{672}\)
Study well ! >_<
