Giải thích các bước giải:

$\begin{aligned}
& \text{Ta có:} \\
& A(x) = 8x^4 - 5x^3 + x^2 - \dfrac{1}{3} \\
& B(x) = x^4 - 2x^3 + x^2 - 5x - \dfrac{2}{3} \\
\\
& \text{a) Tính } A(x) + B(x): \\
& A(x) + B(x) = \left(8x^4 - 5x^3 + x^2 - \dfrac{1}{3}\right) + \left(x^4 - 2x^3 + x^2 - 5x - \dfrac{2}{3}\right) \\
& A(x) + B(x) = (8x^4 + x^4) + (-5x^3 - 2x^3) + (x^2 + x^2) - 5x + \left(-\dfrac{1}{3} - \dfrac{2}{3}\right) \\
& A(x) + B(x) = 9x^4 - 7x^3 + 2x^2 - 5x - \dfrac{3}{3} \\
& A(x) + B(x) = 9x^4 - 7x^3 + 2x^2 - 5x - 1 \\
\\
& \text{b) Tính } A(x) - B(x): \\
& A(x) - B(x) = \left(8x^4 - 5x^3 + x^2 - \dfrac{1}{3}\right) - \left(x^4 - 2x^3 + x^2 - 5x - \dfrac{2}{3}\right) \\
& A(x) - B(x) = 8x^4 - 5x^3 + x^2 - \dfrac{1}{3} - x^4 + 2x^3 - x^2 + 5x + \dfrac{2}{3} \\
& A(x) - B(x) = (8x^4 - x^4) + (-5x^3 + 2x^3) + (x^2 - x^2) + 5x + \left(-\dfrac{1}{3} + \dfrac{2}{3}\right) \\
& A(x) - B(x) = 7x^4 - 3x^3 + 5x + \dfrac{1}{3}
\end{aligned}$