a) $$5x + (-3x) = 5x - 3x = 2x$$
б) $$(-4a) + 5a = 5a - 4a = a$$
в) $$6ab + (-6ab) = 6ab - 6ab = 0$$
г) $$\frac{1}{2}a^2 + \left(-\frac{1}{4}a^2\right) = \frac{1}{2}a^2 - \frac{1}{4}a^2 = \frac{2}{4}a^2 - \frac{1}{4}a^2 = \frac{1}{4}a^2$$
д) $$4x + (-2x) + (-5x) = 4x - 2x - 5x = 2x - 5x = -3x$$
e) $$(a^2) + (-3a^2) + 4a^2 = a^2 - 3a^2 + 4a^2 = -2a^2 + 4a^2 = 2a^2$$
Ответ: a) 2x, б) a, в) 0, г) 1/4 a², д) -3x, e) 2a²