4/3×7+4/7×11+4/11×15+4/15×19+4/19×23+4/23×27

Đáp án:

Giải thích các bước giải:

$\dfrac{1}{3.7}+\dfrac{1}{7.11}+\dfrac{1}{11.15}+\dfrac{1}{15.19}+\dfrac{1}{19.23}+\dfrac{1}{23.27}$

$=\dfrac{1}{3}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{23}+\dfrac{1}{23}-\dfrac{1}{27}$

$=\dfrac{1}{3}-\left (\dfrac{1}{7}-\dfrac{1}{7}+\dfrac{1}{11}-\dfrac{1}{11}+\dfrac{1}{15}-\dfrac{1}{15}+\dfrac{1}{19}-\dfrac{1}{19}+\dfrac{1}{23}-\dfrac{1}{23} \right )-\dfrac{1}{27}$

$=\dfrac{1}{3}-\dfrac{1}{27}$

$=\dfrac{9}{27}-\dfrac{1}{27}$

$=\dfrac{8}{27}$

Chúc em học tốt.