6*. Разложите на множители: 25а²- (a+3)²

$$25a^2 - (a + 3)^2 = (5a)^2 - (a + 3)^2 = (5a - (a + 3))(5a + (a + 3)) = (5a - a - 3)(5a + a + 3) = (4a - 3)(6a + 3) = 3(4a - 3)(2a + 1)$$ Ответ: $$3(4a - 3)(2a + 1)$$