Đặt P = ... ( biểu thức đề bài ) 

Nhận xét: Với \(k\inℕ^∗\) ta có: 

\(\frac{k+2}{k!+\left(k+1\right)!+\left(k+2\right)!}=\frac{k+2}{k!+\left(k+1\right).k!+\left(k+2\right).k!}=\frac{k+2}{2.k!\left(k+2\right)}=\frac{1}{2.k!}\)

\(\Rightarrow\)\(P=\frac{1}{2.1!}+\frac{1}{2.2!}+...+\frac{1}{2.6!}=\frac{1}{2}\left(1+\frac{1}{2}+...+\frac{1}{720}\right)=...\)

*  =1/3 - 5/3 + 3/2

= 1/6

*  = 7/23 .( -7/2)

=-49/46

1 + 2 + 3 + 5 + 6 + 7 - 7 - 6 - 5 - 3 - 2 - 1

= ( 1 - 1 ) + ( 2 - 2 ) + ( 3 - 3 ) + ( 5 - 5 ) + ( 6 - 6 ) + ( 7 - 7 )

= 0

nha

kết quả của mình là bằng 0

= (1/7+7/1)+(2/6+6/2)+(3/5+5/3)+4/4

= 7/1/7+3/1/3+2/4/15+1

= 13/26/35

b: \(B=\dfrac{5}{2}-\dfrac{7}{2}+\dfrac{3}{8}+\dfrac{6}{8}+\dfrac{-6}{11}-\dfrac{5}{11}=-2-1+\dfrac{9}{8}=\dfrac{9}{8}-3=-\dfrac{15}{8}\)

c: \(C=\left(\dfrac{4}{3}+\dfrac{7}{3}+\dfrac{1}{3}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=4+1=5\)

d: \(D=\dfrac{4}{19}\left(\dfrac{-5}{6}-\dfrac{7}{12}\right)-\dfrac{40}{57}\)

\(=\dfrac{4}{19}\cdot\dfrac{-17}{12}-\dfrac{40}{57}=-1\)

e: \(E=\dfrac{1}{3}\left(\dfrac{4}{5}-\dfrac{9}{5}\right)+\dfrac{2}{3}=\dfrac{2}{3}-\dfrac{1}{3}=\dfrac{1}{3}\)

a, \(\dfrac{3}{5}\) \(\times\) \(\dfrac{6}{7}\) + \(\dfrac{3}{5}\) : 7 + \(\dfrac{6}{5}\)

= \(\dfrac{3}{5}\) \(\times\) \(\dfrac{6}{7}\) + \(\dfrac{3}{5}\) \(\times\) \(\dfrac{1}{7}\) + \(\dfrac{6}{5}\)

= \(\dfrac{3}{5}\) \(\times\) ( \(\dfrac{6}{7}\) + \(\dfrac{1}{7}\)) + \(\dfrac{6}{5}\)

= \(\dfrac{3}{5}\) + \(\dfrac{6}{5}\)

= \(\dfrac{9}{5}\) 

b, 2018 \(\times\) ( \(\dfrac{1}{2}\) + \(\dfrac{1212}{2424}\))

= 2018 \(\times\) ( \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\))

= 2018 \(\times\)1

= 2018

a) 3/5 x 6/7 + 3/5 x 1/7 + 6/5

3/5 x ( 6/7 + 1/7 ) + 6/5

3/5 x 7/7 + 6/5 

3/5 x 1 + 6/5

3/5 + 6/5 

9/5

b) 2018 x ( 1/2 + 1212/ 2424 )

2018 x ( 1/2 + 12/24 )

2018 x ( 1/2 + 1/2 )

2018 x 2/2

2018 x 1

2018

Học tốt

A)   (-3/4 + 5/13):2/7-(2/1/2+8/13):2/7

\(=\)

\(=\)

B và C đâu bạn

= 51/20

----------------------------------

= 3/14

------------------------------------

= 4/7 - 2/7 

= 2/7

--------------------------------------

= 17/45

---------------------------------------

= 2/3 

--------------------------------------

= 2 x 1/4 

= 1/2