Question

A=\(\dfrac{5}{13}\). \(\dfrac{5}{7}\)+ \(\dfrac{-20}{41}\)+ \(\dfrac{8}{13}\)+ \(\dfrac{-21}{41}\)

B= \(\dfrac{5}{7}\). \(\dfrac{2}{11}\)+ \(\dfrac{5}{7}\). \(\dfrac{12}{11}\)- \(\dfrac{5}{7}\). \(\dfrac{7}{11}\)

C=\(\dfrac{-2}{3}\)+ \(\dfrac{-5}{7}\)+ \(\dfrac{2}{3}\)+ \(\dfrac{-2}{7}\)

Answer 1

Giải:

a) \(A=\dfrac{5}{13}.\dfrac{5}{7}+\dfrac{-20}{41}+\dfrac{5}{13}+\dfrac{-21}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}.\dfrac{5}{7}+\dfrac{5}{13}+\dfrac{-21}{41}+\dfrac{-20}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}\left(\dfrac{5}{7}+1\right)+\dfrac{-41}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}.\dfrac{12}{7}+\left(-1\right)\)

\(\Leftrightarrow A=\dfrac{60}{91}+\left(-1\right)=-\dfrac{31}{91}\)

Vậy ...

b) \(B=\dfrac{5}{7}.\dfrac{2}{11}+\dfrac{5}{7}.\dfrac{12}{11}-\dfrac{5}{7}.\dfrac{7}{11}\)

\(\Leftrightarrow B=\dfrac{5}{7}\left(\dfrac{2}{11}+\dfrac{12}{11}-\dfrac{7}{11}\right)\)

\(\Leftrightarrow B=\dfrac{5}{7}.\dfrac{7}{11}\)

\(\Leftrightarrow B=\dfrac{5}{11}\)

Vậy ...

c) \(C=\dfrac{-2}{3}+\dfrac{-5}{7}+\dfrac{2}{3}+\dfrac{-2}{7}\)

\(\Leftrightarrow C=\left(\dfrac{-2}{3}+\dfrac{2}{3}\right)+\left(\dfrac{-2}{7}+\dfrac{-5}{7}\right)\)

\(\Leftrightarrow C=0+\left(-1\right)=-1\)

Vậy ...

Answer 2

A

Answer 3

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