Question

Tính

1/2+1/3+1/4+1/6+1/10+1/15+...+1/36+1/45

Answer 1

bn ơi bài này ko có 1/4 đâu: 

đặt A=\(\frac{1}{2}+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{36}+\)\(\frac{1}{45}\)

\(\frac{1}{2}A\)=> \(\frac{1}{2}A\)= \(\frac{1}{4}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{72}+\frac{1}{90}\)

\(\frac{1}{2}A\)= \(\frac{1}{4}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\)

\(\frac{1}{2}A\)= \(\frac{1}{4}\)+  \(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-...+\frac{1}{9}-\frac{1}{10}\)

\(\frac{1}{2}A\)= \(\frac{1}{4}+\frac{1}{2}-\frac{1}{10}=\frac{5}{20}+\frac{10}{20}-\frac{2}{20}=\frac{13}{20}\)

=> A = \(\frac{13}{20}:\frac{1}{2}=\frac{13}{10}\)

Chúc bn học tốt !

Answer 2

k cho mk 

Answer 3

nếu là 1/4 thì bài  ni ko tính dc

Answer 4

13/40