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hermom1967

  • one year ago

Please help explain what I did wrong Express the complex number in trigonometric form. -2i

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  1. hermom1967
    • one year ago
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    I got 2(cos 90° + i sin 90°) but that was wrong and I don't understand why.

  2. hermom1967
    • one year ago
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    @satellite73

  3. myininaya
    • one year ago
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    ok cos(90 deg)=0 and sin(90 deg)=1 so you have 2(0+i*1) 2(i*1) 2(i) 2i

  4. myininaya
    • one year ago
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    but you wanted -2i

  5. myininaya
    • one year ago
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    why don't you just change 2 to -2

  6. myininaya
    • one year ago
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    or you could go with changing the angle from 90 deg to 270 deg since sin will be negative 1there

  7. myininaya
    • one year ago
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    let me know if you need more assistance @hermom1967

  8. hermom1967
    • one year ago
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    So it would be 2(cos 270° + i sin 270°)?

  9. hermom1967
    • one year ago
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    Is that because it's in a different quadrant?

  10. myininaya
    • one year ago
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    right since cos(270 deg)=0 and sin(270 deg)=-1 so you would have 2(0+i[-1]) =2[i[-1]] =2[-i] =-2i

  11. myininaya
    • one year ago
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    also have you ever graphed things in the form a+bi?

  12. hermom1967
    • one year ago
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    No

  13. myininaya
    • one year ago
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    we have a is 0 which means we don't go left or right any but b is -2 which means we have to go down 2 units

  14. myininaya
    • one year ago
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    |dw:1432867663223:dw|

  15. hermom1967
    • one year ago
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    Okay, I understand that

  16. myininaya
    • one year ago
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    you can think of a+bi as if you are plotting points (a,b)

  17. myininaya
    • one year ago
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    you know when graphing

  18. myininaya
    • one year ago
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    |dw:1432867746418:dw|

  19. myininaya
    • one year ago
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    and yeah you could have chose the angle to be 90 deg if you made r negative like you could have done -2(cos(90)+isin(90))

  20. hermom1967
    • one year ago
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    Okay, thank you so much! Now to be able to retain that... LOL

  21. myininaya
    • one year ago
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    I think it will get a little easier when you guys go over plotting things in form a+bi or plotting also polar coordinates, you know where you plot things in the form (r,theta)

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