Question

Đề: Tính giá trị biểu thức

^{\(A=\dfrac{4}{1.2}+\dfrac{4}{2.3}+\dfrac{4}{3.4}+...+\dfrac{4}{2014.2015}\)}

Answer 1

Mình k ghi lại đề nhé!~~

\(A=\dfrac{4}{1}.\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{2014.2015}\right)\)

\(A=\dfrac{4}{1}.\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{2014}-\dfrac{1}{2015}\right)\)

\(A=\dfrac{4}{1}.\left(1-\dfrac{1}{2015}\right)\)

\(A=\dfrac{4}{1}.\left(\dfrac{2015-1}{2015}\right)\)

\(A=\dfrac{4}{1}.\dfrac{2014}{2015}\)

\(A=3,998014888\)

\(A\approx4\)