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Why this signal is linear?

  1. Apr 24, 2009 #1
    hello,
    y(t)=[cos(3t)]*x(t)
    x1(t) -> y1(t)=[cos(3t)]*x1(t)
    x2(t) -> y2(t)=[cos(3t)]*x2(t)
    x3(t) = a*x1(t)+b*x2(t)
    x3(t) -> y3(t)=[cos(3t)]*x3(t)=[cos(3t)]*(a*x1(t)+b*x2(t))=
    =[cos(3t)]*(a*[cos(3t)]*x1(t)+b*[cos(3t)]*x2(t))
    y3(t) not equal a*y1(t)+b*y2(t) but the answers in the book said that
    the system is linear? why? am i wrong or there's a mistake in the book?
     
  2. jcsd
  3. Apr 24, 2009 #2
    Check out the last two lines again. You've got a mistake there...
     
  4. Apr 24, 2009 #3
    i found the mistake, thanks
     
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