Bài 1: Ta chỉ cần bỏ ngoặc rồi cộng hai phân số để ra kết quả là số tự nhiên là xong

Bài 2:

A = \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+............+\frac{1}{2003.2004}\)

A = \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-.............-\frac{1}{2003}+\frac{1}{2003}-\frac{1}{2004}\)

A = \(1-\frac{1}{2004}\)

A = \(\frac{2004}{2004}-\frac{1}{2004}=\frac{2003}{2004}\)

Mk làm mẫu 1 bài nha 

Bài 1 :

a, = (1/4+3/4) - (5/13+8/13)+2/11

    = 1 - 1 + 2/11

    = 2/11

Tk mk nha

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2003.2004}\)

\(\Leftrightarrow A=1\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2003}-\frac{1}{2004}\right)\)

\(\Leftrightarrow A=1\left(1-\frac{1}{2004}\right)\)

\(\Leftrightarrow A=\frac{2003}{2004}\)

a,  -3/4 + 3/7 + -1/4 + 4/9 + 4/7

=\(\left(\frac{-3}{4}+\frac{-1}{4}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{4}{9}\)

=\(-1+1+\frac{4}{9}\)

=\(\frac{4}{9}\)

b, -7/9 x 4/11 + -7/9 x 7/11 + 5 và 7/9 

\(=\frac{7}{9}x\frac{-4}{11}+\frac{7}{9}x\frac{-7}{11}+5x\frac{7}{9}\)

\(=\frac{7}{9}x\left(\frac{-4}{11}+\frac{-7}{11}+5\right)\)

\(=\frac{7}{9}x4\)

\(=\frac{28}{9}\)

c, ( 21/31 + 2013/6039 ) - ( 44/53 - 10/31) - /53

a)(1/4+3/4)-(5/13+8/13)+2/11=1-1+2/11=2/11

b)(21/31+10/31)-16/7+(44/53+9/53)=1+1-16/7=14/7-16/7=-2/7

bằng2/11

         -16/7

a, \(\left(\frac{1}{4}+\frac{-5}{13}\right)+\left(\frac{2}{11}+\frac{-8}{13}+\frac{3}{4}\right)\)

\(=\left(\frac{1}{4}-\frac{5}{13}\right)+\left(\frac{2}{11}-\frac{8}{13}+\frac{3}{4}\right)\)

\(=\frac{1}{4}-\frac{5}{13}+\frac{2}{11}-\frac{8}{13}+\frac{3}{4}=1-1+\frac{2}{11}=\frac{2}{11}\)( vì \(\left(\frac{1}{4}+\frac{3}{4}\right)+\left(-\frac{5}{13}-\frac{8}{13}+\frac{2}{11}\right)\))

b, \(\left(\frac{21}{31}+\frac{-16}{7}\right)+\left(\frac{44}{53}+\frac{10}{31}\right)+\frac{9}{53}\)

\(=\frac{21}{31}-\frac{16}{7}+\frac{44}{53}+\frac{10}{31}+\frac{9}{53}\)

\(=1-\frac{16}{7}+1=\frac{7}{7}-\frac{16}{7}+\frac{7}{7}=-\frac{2}{7}\)

Câu 1:

\(=\dfrac{21}{31}+\dfrac{1}{3}-\dfrac{44}{53}+\dfrac{10}{31}-\dfrac{9}{53}=\dfrac{1}{3}\)

Câu 2:

1: =>1,3x=-1,31

=>130x=-131

=>x=-131/130

2: =>(4,5-2x)=11/14:(-11/7)=-7/14=-1/2=-0,5

=>2x=5

=>x=5/2

a,  -3/4 + 3/7 + -1/4 + 4/9 + 4/7

=

=

=

b. \(\dfrac{-7}{9}.\dfrac{4}{11}+\dfrac{-7}{9}.\dfrac{7}{11}+\dfrac{52}{9}\)

= \(\dfrac{-7}{9}.\left(\dfrac{4}{11}+\dfrac{7}{11}\right)+\dfrac{52}{9}\)

= \(\dfrac{-7}{9}.1+\dfrac{52}{9}\)

= \(\dfrac{-7}{9}+\dfrac{52}{9}\)

= \(\dfrac{45}{9}\)

Chúc bạn học tốt!! ^^

\(a\)) \(\dfrac{-3}{4}+\dfrac{3}{7}+\dfrac{-1}{4}+\dfrac{4}{9}+\dfrac{4}{7}\)

\(=\left(\dfrac{-3}{4}+\dfrac{-1}{4}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{4}{9}\)

\(=-1+1+\dfrac{4}{9}\)

\(=0+\dfrac{4}{9}=\dfrac{4}{9}\)