Ta có: \(a=\frac13-\frac34-\frac35+\frac{1}{72}-\frac29-\frac{1}{36}+\frac{1}{15}\)

\(=\left(\frac13-\frac35+\frac{1}{15}\right)+\left(-\frac34-\frac29-\frac{1}{36}+\frac{1}{72}\right)\)

\(=\left(\frac{5}{15}-\frac{9}{15}+\frac{1}{15}\right)+\left(-\frac{54}{72}-\frac{16}{72}-\frac{2}{72}+\frac{1}{72}\right)\)

\(=\frac{-3}{15}+\frac{-71}{72}=\frac{-1}{5}-\frac{71}{72}=\frac{-72}{360}-\frac{355}{360}=-\frac{427}{360}\)

\(\frac{a}{b}+\frac{-a}{b}+1=\frac{a+\left(-a\right)}{b}+1=0+1=1\)

Câu tương tự có            

\(\frac{1}{3}-\frac{3}{4}-\frac{-3}{5}+\frac{1}{72}-\frac{2}{9}-\frac{1}{36}+\frac{1}{15}\)

\(=\left\{\frac{1}{3}+\frac{3}{5}+\frac{1}{15}\right\}\)\(-\left\{\frac{3}{4}+\frac{2}{9}+\frac{1}{36}\right\}\)\(+\frac{1}{72}\)

\(=1-1+1+\frac{1}{72}\)

\(=\frac{1}{72}\)

Bạn nhờ mik giúp thì phải nhớ tíck mik đó

A=1/3-3/4-(-3/5)+1/72-2/9-1/36+1/15

A=(1/3+3/5+1/15)-(3/4+2/9+1/36)+1/72

A=1-1+1+1/72=1/72

k mình nha

\(A=\frac{1}{3}-\frac{3}{4}-\frac{-3}{5}+\frac{1}{72}-\frac{2}{9}-\frac{1}{36}+\frac{1}{15}\)

\(\Rightarrow A=\frac{1}{3}+\frac{-3}{4}+\frac{3}{5}+\frac{1}{72}+\frac{-2}{9}+\frac{-1}{36}+\frac{1}{15}\)

\(\Rightarrow A=\left(\frac{1}{3}+\frac{3}{5}+\frac{1}{15}\right)+\left(\frac{-3}{4}+\frac{-2}{9}+\frac{-1}{36}\right)+\frac{1}{72}\)

\(\Rightarrow A=1+\left(-1\right)+\frac{1}{72}\)

\(\Rightarrow A=0+\frac{1}{72}\)

\(\Rightarrow A=\frac{1}{72}\)

c/
C = 1/100-1/100-1/99-1/99-1/98-1/98-1/97-..........-1/3-1/2-1/2-1/1
C = 1/100-1/100-1/1
C = 0-1/1
C = -1

a,=(1/3+3/5+1/15)+(3/4+-1/36)+(1/72-2/9)=1+26/36-15/72=1+(52-15)/72=1+37/72=109/72

b,=1/100-(1/1x2+1/2x3+...+1/97x98+1/98x99+1/99x100)

   =1/100-(1/1-1/2+1/2-1/3+...+1/97-1/98+1/98-1/99+1/99-1/100)

   =1/100-(1/1-1/100)=1/100-99/100=-98/100=-49/50

chỉ có mk mk giải thôi đó l-i-k-e đi

mình cũng đang bí bài này

me too