Re: [理工] [通訊]-最大振幅

[ntust661 (Enstchuldigung~)]

※ 引述《aipc (...)》之銘言：
: 某調幅訊號為x(t)=2(1+3cos(6πt))cos(24πt)
: 則訊號 x^2(t)的最大振幅為?
: ANS：64
:    謝謝



   x(t) = 2 [ 1 + 3 cos(6πt) (cos24πt) ]



   x(t) = 2 [ 1 + 3 ( cos(30πt) + cos(18πt) ) ]



   x'(t) =  2 [ - 3 ( 30π sin(30πt) + 18π sin(18πt) )] = 0



   30πsin(30πt) + 18π sin(18πt) = 0


   5 sin(30πt) + 3 sin(18πt) = 0


   3 sin(18πt) = - 5 sin(30πt)


   t = 0


   其他解要數值解了XDD



   x(0) =  2 ( 1  +   3 )


   2
  x (0) =   64



--

--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 122.122.222.25
→ cha122977:題目抄錯喔...x(t)=2(1+3cos(6πt)) X cos(24πt)...