Question

[Tạ Uy Vũ]

3/1x2+3/2x3+3/3x4...+3/14x15=?

Giúp mình với nhé,mình cần gấp lắm.

Answer 1

[kudo shinichi]

\(\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{14.15}\)

\(=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{14.15}\right)\)

\(=3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{14}-\frac{1}{15}\right)\)

\(=3.\left(1-\frac{1}{15}\right)\)

\(=3.\frac{14}{15}\)

\(=\frac{14}{5}\)

Answer 2

[Tạ Uy Vũ]

Cảm ơn bạn rất nhiều nhé

:D