Question

a) A = 5/2*1 + 4/1*11 + 3/11*2 + 1/2*15 + 13/15*4

b)B =  2/12 + 2/20 + 2/30 + 2/42 + 2/56 + 2/72 + 2/90

Answer 1

a,58,25974026

b, 7/15

Answer 2

a) \(\frac{A}{7}=\frac{5}{2\times7}+\frac{4}{7\times11}+\frac{3}{11\times14}+\frac{1}{14\times15}+\frac{13}{15\times28}\)

\(\frac{A}{7}=\frac{7-2}{2\times7}+\frac{11-4}{7\times11}+\frac{14-11}{11\times14}+\frac{15-14}{14\times15}+\frac{28-15}{15\times28}\)

\(\frac{A}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}=\frac{1}{2}-\frac{1}{28}=\frac{13}{28}\)

\(A=7.\frac{13}{28}=\frac{13}{4}\)

Answer 3

ban loan dung

Answer 4

a,13/4

b,7/15