| Line 6: | Line 6: | ||
For any <math>x_{1}(t) \; \rightarrow \; y_{1}(t)</math> and <math>x_{2}(t) \; \rightarrow \; y_{2}(t)</math> | For any <math>x_{1}(t) \; \rightarrow \; y_{1}(t)</math> and <math>x_{2}(t) \; \rightarrow \; y_{2}(t)</math> | ||
| − | + | <DIV CLASS="indented"> | |
and any complex constants <math>a</math> and <math>b</math> | and any complex constants <math>a</math> and <math>b</math> | ||
| − | + | </DIV> | |
then | then | ||
| Line 18: | Line 18: | ||
and "conveniently": | and "conveniently": | ||
| − | <math>e^{2jt} \; + \; e^{-2jt} = \cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(-2t)} \; + \; j \sin{(-2t)}</math> <font size="4"> | + | <math>e^{2jt} \; + \; e^{-2jt} = \cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(-2t)} \; + \; j \sin{(-2t)}</math> <font size="4">(by Euler's Formula)</font> |
<math>=\cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(2t)} \; - \; j \sin{(2t)}</math> (<math>\cos{(-x)}=\cos{(x)}</math> and <math>\sin{(-x)}=-\sin{(x)}</math>) | <math>=\cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(2t)} \; - \; j \sin{(2t)}</math> (<math>\cos{(-x)}=\cos{(x)}</math> and <math>\sin{(-x)}=-\sin{(x)}</math>) | ||
Revision as of 20:29, 16 September 2008
Problem
A linear system’s response to $ e^{2jt} $ is $ te^{-2jt} $, and its response to $ e^{-2jt} $ is $ te^{2jt} $. What is the system’s response to $ cos(2t) $?
Solution
If the system is linear, then the following is true:
For any $ x_{1}(t) \; \rightarrow \; y_{1}(t) $ and $ x_{2}(t) \; \rightarrow \; y_{2}(t) $
and any complex constants $ a $ and $ b $
then
$ ax_{1}(t) \; + \; bx_{2}(t) \; \rightarrow \; ay_{1}(t) \; + \; by_{2}(t) $
and "conveniently":
$ e^{2jt} \; + \; e^{-2jt} = \cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(-2t)} \; + \; j \sin{(-2t)} $ (by Euler's Formula)
$ =\cos{(2t)} \; + \; j \sin{(2t)} \; + \; \cos{(2t)} \; - \; j \sin{(2t)} $ ($ \cos{(-x)}=\cos{(x)} $ and $ \sin{(-x)}=-\sin{(x)} $)
$ =2\cos{(2t)} $
