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![](https://rs.olm.vn/images/avt/0.png?1311)
1.khang dinh A,B,D dung
2,x-(1-x)=5+(-1+x)
x-1+x=5-1+x
2x-1=4+x
2x-x=4+1
x=5
Vay x=5
co bai kho hoi mik nhe
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có: \(\frac{a}{b}+\frac{a}{c}=\frac{ac+ab}{bc}=\frac{a\left(b+c\right)}{bc}=\frac{a.a}{bc}\) (thay b+c = a) (1)
\(\frac{a}{b}\times\frac{a}{c}=\frac{a.a}{bc}\) (2)
Từ (1) và (2) suy ra: \(\frac{a}{b}+\frac{a}{c}=\frac{a}{b}\times\frac{a}{c}\) (đpcm)
b) \(c=a+b\)\(\Rightarrow\)\(a=c-b\)
Ta có: \(\frac{a}{b}-\frac{a}{c}=\frac{ac-ab}{bc}=\frac{a\left(c-b\right)}{bc}=\frac{a^2}{bc}\) (thay c-b = a) (3)
\(\frac{a}{b}\times\frac{a}{c}=\frac{a^2}{bc}\) (4)
Từ (3) và (4) suy ra: \(\frac{a}{b}-\frac{a}{c}=\frac{a}{b}\times\frac{a}{c}\) (đpcm)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(4,VT=-a+b+c-a+b-c+a-b-c=-a+b-c=-\left(a-b+c\right)=VP\\ 5,M=-a+b-b-c+a+c-a=-a\\ M>0\Rightarrow-a>0\Rightarrow a< 0\)
a)\(\dfrac{a}{b}+\dfrac{a}{c}=\dfrac{ac}{bc}+\dfrac{ab}{bc}=\dfrac{ac+ab}{bc}=\dfrac{a\left(b+c\right)}{bc}=\dfrac{a^2}{bc}\) \(\dfrac{a}{b}.\dfrac{a}{c}=\dfrac{a^2}{bc}\)
\(\Rightarrow\dfrac{a}{b}+\dfrac{a}{c}=\dfrac{a}{b}.\dfrac{a}{c}=\dfrac{a^2}{bc}\)
b)\(\dfrac{a}{b}-\dfrac{a}{c}=\dfrac{ac}{bc}-\dfrac{ab}{bc}=\dfrac{ac-ab}{bc}=\dfrac{a\left(c-b\right)}{bc}=\dfrac{a^2}{bc}\)\(\dfrac{a}{b}.\dfrac{a}{c}=\dfrac{a^2}{bc}\)
\(\Rightarrow\dfrac{a}{b}-\dfrac{a}{c}=\dfrac{a}{b}.\dfrac{a}{c}=\dfrac{a^2}{bc}\)