(2a+3)(6a+2)-6a(2a+13)+8(7a+2)
=12a^2+4a+18a+6-12a^2-78a+56a+16
=(12a^2-12a^2)+(4a+18a+56a-78a)+(16+6)
=0+0+22
=22
所以,不论a是多少,原式都是等于22.