JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    The argument of the complex number\[\frac{13-5i}{4-9i}\]is

    A) \[\frac{\pi }{3}\]                                              

    B) \[\frac{\pi }{4}\]

    C) \[\frac{\pi }{5}\]                              

    D) \[\frac{\pi }{6}\]

    Correct Answer: B

    Solution :

    Key Idea The argument of \[z\] is\[{{\tan }^{-1}}\frac{y}{x}\]. Let          \[z=\frac{13-5i}{4-9i}\frac{4+9i}{4+9i}\]                    \[=\frac{52+117i-20i-45{{i}^{2}}}{{{(4)}^{2}}-{{(9i)}^{2}}}\]                    \[=\frac{532+97i+45}{16+81}\]                    \[=\frac{97+97i}{97}\] \[\Rightarrow \]        \[z=1+i\] \[\therefore \]\[\arg (z)={{\tan }^{-1}}\left( \frac{1}{1} \right)=\frac{\pi }{4}\].


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