第1章 1.3

(1)

$A = 7x^2 + x - 3$ $B = 3x^2 + 4x - 5$

$A + B = 10x^2 + 5x - 8$ $A - B = 4x^2 - 3x + 2$

(2)

$A = x^2 - 7xy + 5y^2$ $B = 4x^2 - 3xy + 2y^2$

$A + B = 5x^2 - 10xy + 7y^2$ $A - B = -3x^2 - 4xy + 3y^2$

(3)

$A = \dfrac{a^2}{3} + \dfrac{1}{2}ab - b^2$ $B = \dfrac{a^2}{2} - ab + \dfrac{b^2}{2}$

$A + B = \dfrac{5}{6}a^2 - \dfrac{1}{2}ab - \dfrac{1}{2}b^2$ $A - B = -\dfrac{1}{6}a^2 + \dfrac{3}{2}ab - \dfrac{3}{2}b^2$

(4)

$A = 2x^3 + x^2y - 2y^3$ $B = 2x^2y + 3xy^2$

$A + B = 2x^3 + 3x^2y + 3xy^2 - 2y^3$ $A - B = 2x^3 - x^2y - 3xy^2 - 2y^3$