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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,(-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.
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= \(\dfrac{-3}{5}-\dfrac{-4}{5}+\dfrac{-9}{10}\)
A = \(\dfrac{-7}{10}\)
a) \(\frac{25}{9}-\frac{12}{13}x=\frac{7}{9}\)
=> \(\frac{12}{13}x=\frac{25}{9}-\frac{7}{9}=\frac{18}{9}=2\)
=> \(x=2:\frac{12}{13}=2\cdot\frac{13}{12}=\frac{13}{6}\)
b) \(x:\frac{13}{3}=-2,5\)
=> \(x:\frac{13}{3}=-\frac{5}{2}\)
=> \(x=\left(-\frac{5}{2}\right)\cdot\frac{13}{3}=-\frac{65}{6}\)
c) \(\frac{x}{3}-\frac{1}{4}=-\frac{5}{6}\)
=> \(\frac{4x-3}{12}=-\frac{10}{12}\)
=> 4x - 3 = -10
=> 4x = -10 + 3 = -7
=> x = -7/4
Bài 2 :
\(A=a\cdot\frac{1}{3}+a\cdot\frac{1}{4}-a\cdot\frac{1}{6}=a\left(\frac{1}{3}+\frac{1}{4}-\frac{1}{6}\right)=a\cdot\frac{5}{12}\)
Thay a = -3/5 vào biểu thức ta có : \(A=\left(-\frac{3}{5}\right)\cdot\frac{5}{12}=\frac{-3}{12}=\frac{-1}{4}\)
\(B=b\cdot\frac{5}{6}+b\cdot\frac{3}{4}-b\cdot\frac{1}{2}=b\left(\frac{5}{6}+\frac{3}{4}-\frac{1}{2}\right)=b\cdot\frac{13}{12}\)
Thay b = 12/13 vào ta được kết quả là 1
a ) \(\frac{25}{9}-\frac{12}{13}\cdot x=\frac{7}{9}\)
\(\Rightarrow\frac{12}{13}\cdot x=\frac{25}{9}-\frac{7}{9}=\frac{18}{9}=2\)
\(\Rightarrow x=2\div\frac{12}{13}=2\cdot\frac{13}{12}=\frac{13}{6}\)
Vậy ...
b ) \(x\div\frac{13}{3}=-\frac{5}{2}\)
\(\Rightarrow x\div\frac{13}{3}=-\frac{5}{2}\)
\(\Rightarrow x=\left(-\frac{5}{2}\right)\cdot\frac{13}{3}=-\frac{65}{6}\)
Vậy ..
c ) \(\frac{x}{3}-\frac{1}{4}=-\frac{5}{6}\)
\(\Rightarrow\frac{4x-3}{12}=-\frac{10}{12}\)
\(\Rightarrow4x-3=-10\)
\(\Rightarrow4x=-10+3=-7\)
\(\Rightarrow x=-\frac{7}{4}\)
Vậy ....