1-5 已知f(t),为求 ((t)_(0)-at) 应按下列哪种运算求得正确结果(式中t0、a都-|||-为正值)?-|||-(1) f(-at) 左移t0-|||-(2)f(at)右移t0-|||-(3)f(at)左移 dfrac (t0)(a)-|||-(4) f(-at) 右移 dfrac (t0)(a)