... -2t ] = De -2t , Vy D[ bte -2t ] = b (1 - 2t )e -2t D [ bte -2t ] = 4b (1 - 2t )e -2t D -2t ] = -2e -2t b (4t - + - 6t )e -2t = -2e -2t - be -2t = -2e -2t , cú b = v Nờn Hay yf (t ) = 2te -2t ... - 2c2 e -2t (2. 23b) Cỏc iu kin u [xem phng trỡnh (2. 21) vi n = 2] & y n ( 0) = v y n ( 0) = Trong phng trỡnh (2. 23a) v (2. 23b) cho t = 0, th cỏc iu kin u vo, ta cú = c1 + c2 = -c1 - 2c2 (2. 24) ... hm phng trỡnh (2. 12a), ta cú & y0 (t ) = -2ce -2t cos(6t + q ) - 6ce -2t sin(6t + q ) (2. 12b) Cho t = phng trỡnh (2. 12a) v (2. 12b), ri thay iu kin u vo, ta cú = cosq 16,78 = -2c cosq - 6c sin...