4. Упростите выражение. a) (4a-b) (a-6b) + a (25b-3a): 5) 2c (5c-3)-(c-2) (c-4): 8) (y-3) (5)-(4-y) (y+6)

a) $$(4a-b)(a-6b)+a(25b-3a) = 4a^2 - 24ab - ab + 6b^2 + 25ab - 3a^2 = a^2 + 6b^2$$

Ответ: $$a^2 + 6b^2$$

б) $$2c(5c-3) - (c-2)(c-4) = 10c^2 - 6c - (c^2 - 4c - 2c + 8) = 10c^2 - 6c - c^2 + 6c - 8 = 9c^2 - 8$$

Ответ: $$9c^2 - 8$$

в) $$(y-3)(5-y) - (4-y)(y+6) = 5y - y^2 - 15 + 3y - (4y + 24 - y^2 - 6y) = 8y - y^2 - 15 - 4y - 24 + y^2 + 6y = 10y - 39$$

Ответ: $$10y - 39$$