Question

2/1x3 + 2/3x5 + 2/5x7 + 2/7x9 +2/9x11

Answer 1

\(\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+\dfrac{2}{9\times11}\\ =\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\right)\\ =1-\dfrac{1}{11}\\ =\dfrac{10}{11}\)

Answer 2

mình làm theo công thức lớp 6 lên lớp 6 bạn tự hiểu