2 wrong, equal when c=0, for the above reasons;

3 pairs, the nature of inequality can be proved by mathematical induction;

4 pairs, obtained by adding two formulas by C; b-d；

Used as a difference comparison method

Because (x+1) (x+2)-(x-3) (x+6) = x2+3x+2-(x2+3x-18) = 20 > 0.

So (x+ 1)(x+2)>(x-3)(x+6)