一.计算(x-3)(x-7)+42123 -124*122(2a+b+3)(2a+b-3)（x+2y-1）（x-2y+1）-（x-2y-1).(a^2+3)(a-2)-a(a^2-2a-2) (2).(3/4a^6x^2+6/5a^3x^4-0.9ax^3)÷3/5ax^2 1）^25a^2b-[3ab^2-(4ab^2-2a^2b)](-3a-2)(3a-2) (3+2a)(...