giải hộ mik cái
a; =(1/4+3/4)+5/9=1+5/9=14/9
b: =(7/12)+(7/8+9/8)=2+7/12=31/12
c: =(2/3+4/3)+(1/5+4/5)=2+1=3
a; =(1/4+3/4)+5/9=1+5/9=14/9
b: =(7/12)+(7/8+9/8)=2+7/12=31/12
c: =(2/3+4/3)+(1/5+4/5)=2+1=3
a)\(\dfrac{1}{4}+\dfrac{5}{9}+\dfrac{3}{4}=\left(\dfrac{1}{4}+\dfrac{3}{4}\right)+\dfrac{5}{9}\) \(=\dfrac{4}{4}+\dfrac{5}{9}=1+\dfrac{5}{9}=\dfrac{9}{9}+\dfrac{5}{9}=\dfrac{14}{9}\)
b) \(\left(\dfrac{7}{12}+\dfrac{7}{8}\right)+\dfrac{9}{8}=\dfrac{7}{12}+\dfrac{7}{8}+\dfrac{9}{8}=\dfrac{7}{12}+\left(\dfrac{7}{8}+\dfrac{9}{8}\right)=\dfrac{7}{12}+\dfrac{16}{8}=\dfrac{7}{12}+2=\dfrac{7}{12}+\dfrac{24}{12}=\dfrac{31}{12}\)
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