Question

Giúp mình vs mn

Answer 1

\(\dfrac{x}{x+4}+\dfrac{56-x^2}{x^2-16}=\dfrac{5}{x-4}\) (*)

ĐKXĐ: \(x\ne4\)

(*) \(\Leftrightarrow\dfrac{x^2-4x}{\left(x-4\right)\left(x+4\right)}+\dfrac{56-x^2}{\left(x-4\right)\left(x+4\right)}=\dfrac{5x+20}{\left(x-4\right)\left(x+4\right)}\)

\(\Leftrightarrow\dfrac{56-4x}{\left(x-4\right)\left(x+4\right)}=\dfrac{5x+20}{\left(x-4\right)\left(x+4\right)}\)

\(\Leftrightarrow56-4x=5x+20\)

\(\Leftrightarrow9x=36\)

\(\Leftrightarrow x=4\) ( không thỏa mãn đk )

Vậy phương trình vô nghiệm 

Answer 2

b: Ta có: \(\dfrac{x}{x+4}+\dfrac{56-x^2}{x^2-16}=\dfrac{5}{x-4}\)

Suy ra: \(x^2-4x+56-x^2=5x+20\)

\(\Leftrightarrow5x+20=-4x+56\)

\(\Leftrightarrow9x=36\)

hay x=4(loại)