5/2\(\times\)1=\(\frac{5}{2\times1}hay=\frac{5}{2}\times1\)

\(A=\frac{5}{2\times1}+\frac{4}{1\times11}+\frac{3}{11\times2}+\frac{1}{2\times15}+\frac{13}{15\times4}\)

      \(=\frac{5}{2}+\frac{4}{11}+\frac{3}{22}+\frac{1}{30}+\frac{13}{60}\)

        \(=\frac{13}{4}\)hoặc 3,25

Vậy A = 13/4 hoặc 3,25

Đặt \(A=\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}+\dfrac{13}{15.4}\)

\(\dfrac{A}{7}=\dfrac{5}{2.7}+\dfrac{4}{7.11}+\dfrac{3}{11.14}+\dfrac{1}{14.15}+\dfrac{13}{15.4}\)

\(\dfrac{A}{7}=\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+...+\dfrac{1}{15}-\dfrac{1}{28}\)

\(\dfrac{A}{7}=\dfrac{1}{2}-\dfrac{1}{28}\)

\(\dfrac{A}{7}=\dfrac{13}{28}\)

\(A=\dfrac{13}{28}.7\)

\(A=\dfrac{13}{4}\)

a) 4,25 x 58,47 + 41,53 x 4,25

= 4,25 x ( 58,47 + 41,53 )

= 4,25 x 100

= 425

nhớ k đúng cho mik nha

B = 7x( 5/2x7 + 4/7x11 + 3/11x14 + 1/14x15 + 13/15x28 )

B = 7x(1/2 - 1/7 + 1/7 - 1/11 +....+ 1/15 - 1/28)

B = 7x(1/2 - 1/28)

B = 7x13/28

B = 13/4

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

B = 7x(1/2 - 1/7 + 1/7 - 1/11 +.....+ 1/15 - 1/28)

B = 7x(1/2 - 1/28)

B = 7 x 13/28

B = 13/4

Ai k mk mk k lại!!

bằng 13/4 nhá

có ai kết bạn với tui ko?????

B = 7x( 5/2x7 + 4/7x11 + 3/11x14 + 1/14x15 + 13/15x28 )

B = 7x(1/2 - 1/7 + 1/7 - 1/11 +....+ 1/15 - 1/28)

B = 7x(1/2 - 1/28)

B = 7x13/28

B = 13/4

Ai k mk mk k lai!

13/4 nha bn

13/4 tích mk mk tích lại