Question

tính D = 5x^2-7x+1 / 3x-1 với |x| = 1/2

Answer 1

Ta có:

\(\left|x\right|=\dfrac{1}{2}\)

\(\Rightarrow\left\{{}\begin{matrix}x=\dfrac{1}{2}\\x=-\dfrac{1}{2}\end{matrix}\right.\)

Trường hợp 1: \(x=\dfrac{1}{2}\)

Thay vào D ta có:

\(D=\dfrac{5\cdot\left(\dfrac{1}{2}\right)^2-7\cdot\dfrac{1}{2}+1}{3\cdot\dfrac{1}{2}-1}=-\dfrac{5}{2}\)

Trường hợp 2: \(x=-\dfrac{1}{2}\)

Thay vào D ta có:

\(D=\dfrac{5\cdot\left(-\dfrac{1}{2}\right)^2-7\cdot-\dfrac{1}{2}+1}{3\cdot-\dfrac{1}{2}-1}=-\dfrac{23}{10}\)