Question

Không quy đồng mẫu các phân số hãy tính hgowpj lí tổng sau:

B= \(\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

PLEASE, HELP ME!

Answer 1

Ta có : 

\(B=\frac{5}{2\cdot1}+\frac{4}{1\cdot11}+\frac{3}{11\cdot2}+\frac{1}{2\cdot15}+\frac{13}{15\cdot4}\)

\(=>\frac{B}{7}=\frac{5}{2\cdot7}+\frac{4}{7\cdot11}+\frac{3}{11\cdot14}+\frac{1}{14\cdot15}+\frac{13}{15\cdot28}\)

\(=>\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(=>\frac{B}{7}=\frac{1}{2}-\frac{1}{28}=\frac{14}{28}-\frac{1}{28}=\frac{13}{28}\)

\(=>B=\frac{13}{28}\cdot7=\frac{13}{4}\)

Answer 2

Khó wá

Answer 3

Hay

Answer 4

B= 5/2.1+4/1.11+3/11.2+1/2.15+13/15.4

B/7= 5/2.7+4/7.11+3/11.14+1/14.15+13/15.28

B/7= 1/2-1/7+1/7-1/11+1/11-1/14+1/14-1/15+1/15-1/28

B/7= 1/2-1/28

B/7= 13/28

B = 13/4