Đáp án:
b) \(\left[ \begin{array}{l}
x = 0\\
x = \dfrac{1}{2}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
A\left( x \right) = 2x - 5{x^2} - \dfrac{5}{2} - x - 2{x^2} + 2{x^3}\\
= 2{x^3} - 7{x^2} + x - \dfrac{5}{2}\\
B\left( x \right) = 3 + 10{x^2} - {x^3} - 3{x^2} - {x^3} - 2x\\
= - 2{x^3} + 7{x^2} - 2x + 3\\
b)M\left( x \right) = A\left( x \right) + B\left( x \right)\\
= 2{x^3} - 7{x^2} + x - \dfrac{5}{2} - 2{x^3} + 7{x^2} - 2x + 3\\
= - x + \dfrac{1}{2}\\
K\left( x \right) = 2x.M\left( x \right) = 0\\
\to 2x\left( {\dfrac{1}{2} - x} \right) = 0\\
\to \left[ \begin{array}{l}
x = 0\\
x = \dfrac{1}{2}
\end{array} \right.
\end{array}\)