题目[题目]计算-|||-(1) (2x+1)(x+3) ;-|||-(2) (m+2n)(3n-m) ;-|||-(3) ((a-1))^2 ;-|||-(4) (a+3b)(a-3b);-|||-(5) (2(x)^2-1)(x-4):-|||-(6) ((x)^2+2x+3)(2x-5)题目解答答案