Question

Tính nhanh:

7/2x3+7/3x4+7/4x5+7/5x6

Answer 1

\(\dfrac{7}{2\times3}+\dfrac{7}{3\times4}+\dfrac{7}{4\times5}+\dfrac{7}{5\times6}\)

= 7 x ( \(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}\) )

= 7 x \(\left(\dfrac{1}{2}-\dfrac{1}{6}\right)\)

= 7 x \(\dfrac{1}{3}=\dfrac{7}{3}\)