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Homework Help: Questions in polar and rectangular i want help

  1. Apr 19, 2010 #1
    Hi



    I want check my answer if correct or not



    write in rectangular form

    1) Z2 = 3e^(-60)i

    2) z3 = 7.19e^-2.13i

    3) z1 = root2 e^(-pi/2)i

    4)z2 = 3e^120i

    5 ) z3 = 6.49e^-2.08i

    ------







    my answer :







    1)

    = 3{cos (-60 ) + i sin ( -60) }

    = 3(cos(1/2) + i sin (-root 3/2 ) }

    = 3(1/2 + - root3/2)

    = 1/2 + - root 3 /6



    2 )

    = 7.19 { cos ( -2.13 ) - i sin (-2.13 ) }

    = 7.19{ 0.999 - -(0.037 ) }

    = 7.182 - 0.266



    3 )



    = root2 { cos (-pi/2) - i sin (-pi / 2 ) }

    = root 2 ( 0- 1 )

    = 0 - root2



    4 )



    = 3{ cos (120) - i sin (120) }

    3(1/2) - ( root 3 /2 )

    = 1/2 - root3/6



    5 )

    6.49 {(cos ( -2.08 ) - i sin ( -2.08 ) i )

    = 6.49 (0.999 ) - ( -0.036 )

    = 6.18 + -236

    =6.18 - 236
     
  2. jcsd
  3. Apr 19, 2010 #2

    LCKurtz

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    Science Advisor
    Homework Helper
    Gold Member

    I will help you on the first one. The first nitpick is that the exponential should be expressed in radian measure.

    [tex] Z_2 =3e^{-\frac {i\pi}{3}}[/tex]
    That step is wrong, cos(-60) isn't equal cos(1/2)...

    which you now sort of fixed...
    and messed up again. What happened to the 3? The cosine of -60 degrees has one value and you have to choose the correct + or -.
     
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