2) (2a+3x) (5a-x)-(a+x) (10a-3x)

Решение: $$(2a+3x)(5a-x) - (a+x)(10a-3x) = 2a(5a-x) + 3x(5a-x) - [a(10a-3x) + x(10a-3x)] = 10a^2 - 2ax + 15ax - 3x^2 - [10a^2 - 3ax + 10ax - 3x^2] = 10a^2 + 13ax - 3x^2 - [10a^2 + 7ax - 3x^2] = 10a^2 + 13ax - 3x^2 - 10a^2 - 7ax + 3x^2 = (10-10)a^2 + (13-7)ax + (-3+3)x^2 = 6ax$$ Ответ: $$6ax$$