Question

Bài `1:P=8/(x^{2}+4x)+5/(x+4)-2/5` với `x≠0 ;x≠-4`

a) Rút gọn `P`

b) Tính giá trị P tại `x=1/2`

Answer 1

tham khảo:

\(P=\)\(\dfrac{8}{x^2+4x}\)+\(\dfrac{5}{x+4}\) - \(\dfrac{2}{x}\)

\(=\) \(\dfrac{8}{x\left(x+4\right)}\)+\(\dfrac{5x}{x\left(x+4\right)}\) - \(\dfrac{2\left(x+4\right)}{x\left(x+4\right)}\)

\(=\) \(\dfrac{8+5x-2x-8}{x\left(x+4\right)}\)

\(=\) \(\dfrac{3}{x\left(x+4\right)}\)

\(=\) \(\dfrac{3}{x+4}\)

Khi \(x =\) \(\dfrac{1}{2}\) thì \(P=\) \(\dfrac{3}{\dfrac{1}{2}+4}\) \(=\) \(\dfrac{2}{3}\)