Giải bài 7.14 trang 33 toán 7 tập 2 kết nối tri thức.
$A + B = 6x^4 – 4x^3 + x - \frac{1}{3} + (-3x^4 – 2x^3 – 5x^2 + x + \frac{2}{3})$
$= 6x^4 – 4x^3 + x - \frac{1}{3} - 3x^4 – 2x^3 – 5x^2 + x + \frac{2}{3}$
$= (6x^4 – 3x^4) + (-4x^3 – 2x^3) – 5x^2 + (x + x) + (- \frac{1}{3} + \frac{2}{3})$
$= 3x^4 - 6x^3 – 5x^2 + 2x + \frac{1}{3}$
$A - B = 6x^4 – 4x^3 + x - \frac{1}{3} - (-3x^4 – 2x^3 – 5x^2 + x + \frac{2}{3})$
$= 6x^4 – 4x^3 + x - \frac{1}{3} + 3x^4 + 2x^3 + 5x^2 - x - \frac{2}{3}$
$= (6x^4 + 3x^4) + (-4x^3 + 2x^3) + 5x^2 + (x - x) + (- \frac{1}{3} - \frac{2}{3})$
$= 9x^4 - 2x^3 + 5x^2 - 1$