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1)
\(A=\dfrac{5}{7}.\dfrac{-4}{13}+\dfrac{5}{7}.\dfrac{7}{13}-\dfrac{5}{13}.\dfrac{3}{7}\)
\(A=\dfrac{5}{7}.\dfrac{-4}{13}+\dfrac{5}{7}.\dfrac{7}{13}-\dfrac{5}{7}.\dfrac{3}{13}\)
\(A=\dfrac{5}{7}.\left(\dfrac{-4}{13}+\dfrac{7}{13}-\dfrac{3}{13}\right)\) (Tính chất phân phối của phép nhân đối với phép cộng)
\(A=\dfrac{5}{7}.0\) (Tính chất nhân với số 0)
\(A=0\)
2)
a) \(A=\dfrac{-6}{5}.\dfrac{1}{2}-\dfrac{-6}{5}.\dfrac{2}{3}+\dfrac{-6}{5}.\dfrac{3}{4}\)
\(A=\dfrac{-6}{5}.\left(\dfrac{1}{2}-\dfrac{2}{3}+\dfrac{3}{4}\right)\)
\(A=\dfrac{-6}{5}.\dfrac{7}{12}\)
\(A=\dfrac{-7}{10}\)
b) \(B=\dfrac{-1}{6}.\dfrac{-3}{7}+\dfrac{4}{3}.\dfrac{-3}{7}-\dfrac{1}{2}.\dfrac{-3}{7}\)
\(B=\dfrac{-3}{7}.\left(\dfrac{-1}{6}+\dfrac{4}{3}-\dfrac{1}{2}\right)\)
\(B=\dfrac{-3}{7}.\dfrac{2}{3}\)
\(B=\dfrac{-2}{7}\)
c) \(C=\dfrac{2013}{2014}.\dfrac{5}{4}+\dfrac{2013}{2014}.\dfrac{1}{6}-\dfrac{2013}{2014}.\dfrac{17}{12}\)
\(C=\dfrac{2013}{2014}.\left(\dfrac{5}{4}+\dfrac{1}{6}-\dfrac{17}{12}\right)\)
\(C=\dfrac{2013}{2014}.0\)
\(C=0\)
a: \(A=a\left(\dfrac{1}{2}-\dfrac{2}{3}+\dfrac{3}{4}\right)=\dfrac{7}{12}a=\dfrac{7}{12}\cdot\dfrac{-6}{5}=\dfrac{-7}{10}\)
b: \(B=b\left(-\dfrac{1}{6}+\dfrac{4}{3}-\dfrac{1}{2}\right)=\dfrac{2}{3}b=\dfrac{2}{3}\cdot\dfrac{-3}{7}=\dfrac{-2}{7}\)
c: \(C=c\left(\dfrac{5}{4}+\dfrac{1}{6}-\dfrac{17}{12}\right)=0\)
A=a.1/3 + a. 1/4 - a. 1/6 với a=-3/5
\(\Rightarrow\frac{-3}{5}.\frac{1}{3}+\frac{-3}{5}.\frac{1}{4}-\frac{-3}{5}.\frac{1}{6}=\frac{-3}{5}.\left(\frac{1}{3}+\frac{1}{4}-\frac{1}{6}\right)=\frac{-3}{5}.\left(\frac{4}{12}+\frac{3}{12}-\frac{2}{12}\right)=\frac{-3}{5}.\frac{9}{12}=\frac{-3.9}{5.12}=\frac{-1.9}{5.4}=\frac{-9}{20}\)
B=b.5/6 + b.3/4 - b.1/2 với b = 12/13
\(\Rightarrow\frac{12}{13}.\frac{5}{6}+\frac{12}{13}.\frac{3}{4}-\frac{12}{13}.\frac{1}{2}=\frac{12}{13}.\left(\frac{5}{6}+\frac{3}{4}-\frac{1}{2}\right)=\frac{12}{13}.\left(\frac{10}{12}+\frac{9}{12}-\frac{6}{12}\right)=\frac{12}{13}.1=\frac{12}{13}\)
C=c.2/3 + c. 3/4 - c. 17/12 với c = 2009/2010
\(\Rightarrow\frac{2009}{2010}.\frac{2}{3}+\frac{2009}{2010}.\frac{3}{4}-\frac{2009}{2010}.\frac{17}{12}=\frac{2009}{2010}.\left(\frac{2}{3}+\frac{3}{4}-\frac{17}{12}\right)=\frac{2009}{2010}.\left(\frac{8}{12}+\frac{9}{12}-\frac{17}{12}\right)=\frac{2009}{2010}.0=0\)
a,(-1).(-2).(-3).(-4).(-5).(-6).(-7)
=-(1.2.3.4.5.6.7)
=-(6.20.42)=-5040
b,(-75).(-27).(-x) với x=4
Thay x vào (-75).(-27).(-x) ,ta có:
(-75).(-4).(-27)=300.(-27)=-8100
c,2.a.b^2 với a=4,b=-6
Thay a=4,b=-6 vào 2.a.b^2 ta có:
2.4.-6^2=8.36=288
Vậy nha:) Bye.
Khi a=-4/5
= > A=-4/5.1/2+(-4/5).1/3+(-4/5).1/4
A=-4/5.(1/2+1/3-1/4)
A=-4/5.7/12
A=-7/15
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