a) Thế \(x=4\) vào biểu thức ta được:
\(A=2\left|4-2\right|-3\left|1-4\right|\\ A=2\left|2\right|-3\left|-3\right|\\ A=2.2-3.3\\ A=4-9\\ A=-5\)
b) Ta có \(\left|x\right|=\dfrac{1}{2}\Rightarrow\left\{{}\begin{matrix}x=\dfrac{1}{2}\\x=-\dfrac{1}{2}\end{matrix}\right.\)
TH1: Thế \(x=\dfrac{1}{2}\) vào biểu thức ta được:
\(B=\dfrac{5.\left(\dfrac{1}{2}\right)^2-7.\dfrac{1}{2}+1}{3.\dfrac{1}{2}-1}\\ B=\dfrac{5.\dfrac{1}{4}-\dfrac{7}{2}+1}{\dfrac{3}{2}-1}\\ B=\dfrac{\dfrac{5}{4}-\dfrac{7}{2}+1}{\dfrac{1}{2}}\\ B=\dfrac{-\dfrac{5}{4}}{\dfrac{1}{2}}\\ B=-\dfrac{5}{2}\)
TH2: Thế \(x=-\dfrac{1}{2}\) vào biểu thức ta được:
\(B=\dfrac{5.\left(-\dfrac{1}{2}\right)^2-7.\left(-\dfrac{1}{2}\right)+1}{3.\left(-\dfrac{1}{2}\right)-1}\\ B=\dfrac{5.\left(\dfrac{1}{2}\right)^2+\dfrac{7}{2}+1}{-\dfrac{3}{2}-1}\\ B=\dfrac{5.\dfrac{1}{4}+\dfrac{7}{2}+1}{-\dfrac{5}{2}}\\ B=\dfrac{\dfrac{5}{4}+\dfrac{7}{2}+1}{-\dfrac{5}{2}}\\ B=\dfrac{23}{\dfrac{4}{-\dfrac{5}{2}}}\\ B=-\dfrac{23}{10}\)
Gửi em.
