Question

\(B = 2x^{3} - \dfrac{1}{3}x^{2} - |x - \dfrac{1}{4}| \) với \(x = \dfrac{1}{2}\)

Answer 1

\(B=2\cdot\left(\dfrac{1}{2}\right)^3-\dfrac{1}{3}\cdot\dfrac{1}{4}-\left|\dfrac{1}{2}-\dfrac{1}{4}\right|\)

\(=2\cdot\dfrac{1}{8}-\dfrac{1}{12}-\dfrac{1}{2}\)

\(=\dfrac{1}{4}-\dfrac{1}{12}-\dfrac{1}{2}\)

\(=\dfrac{3}{12}-\dfrac{1}{12}-\dfrac{6}{12}\)

\(=\dfrac{-1}{3}\)

Answer 2

\(B=2x^3-\dfrac{1}{3}x^2-\left|x-\dfrac{1}{4}\right|\)

Thay \(x=\dfrac{1}{2}\) vào biểu thức ta có:

\(B=2\left(\dfrac{1}{2}\right)^3-\dfrac{1}{3}.\left(\dfrac{1}{2}\right)^2-\left|\dfrac{1}{2}-\dfrac{1}{4}\right|\)

   \(=2.\dfrac{1}{8}-\dfrac{1}{3}.\dfrac{1}{4}-\dfrac{1}{2}\)

   \(=\dfrac{1}{4}-\dfrac{1}{12}-\dfrac{1}{2}\)

   \(=-\dfrac{1}{3}\)