Question

tính:  1/1.2.3+1/2.3.4+1/3.4.5+...+1/98.99.100

Answer 1

=1/1.2.3+1/2.3.4+1/3.4.5+............+1/98.99.100

 $=\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{98.99}-\frac{1}{99.100}\right)$

$=\frac{1}{2}\left(\frac{1}{2}-\frac{1}{9900}\right)$

$=\frac{1}{2}\cdot \frac{4949}{9900}$

$=\frac{4949}{19800}$

Answer 2

cho mình xin lỗi vì đáp án mình gửi lên nó bị lỗi nhá