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2. and

3.has

4.an

5.She

6.a

7. is

Ta có:

(15-x)+(x-12)=7-(-5+x)

=>15-x+x-12=7+5-x

=>3=12-x

=>x=9

8, đk: x≠2; x≠\(\dfrac{3}{4}\)

\(\dfrac{5}{x-2}+\dfrac{6}{3-4x}=0\)

\(\Leftrightarrow\dfrac{5}{x-2}=\dfrac{-6}{3-4x}\)

\(\Leftrightarrow5.\left(3-4x\right)=-6.\left(x-2\right)\)

\(\Leftrightarrow15-20x=-6x+12\)

\(\Leftrightarrow-14x=-3\)

\(\Leftrightarrow x=\dfrac{3}{14}\)( thỏa mãn)

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

\(\Leftrightarrow\dfrac{\left(2x+3\right).7}{21}-\dfrac{3x}{21}=\dfrac{\left(5-x\right).7}{21}\)

\(\Rightarrow14x+21-3x=35-7x\)

\(\Leftrightarrow18x=14\)

\(\Leftrightarrow x=\dfrac{7}{9}\)