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    sorry i just dont get it... edexcel FP1 exercise 1E question 5 (page 18)

    argument of -8-7i

    i end up with 3.86.... answer is somehow -2.42.... help?
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    (Original post by bong)
    sorry i just dont get it... edexcel FP1 exercise 1E question 5 (page 18)

    argument of -8-7i

    i end up with 3.86.... answer is somehow -2.42.... help?
    Draw yourself a diagram of your complex number on an Argand diagram and then mark out the argument of that and then mark the angle you actually work out by doing \mathrm{arctan} \frac{y}{x} and it should become apparent what you need to do to get the argument.
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    Also remember that you'd usually put your answer (theta) between -pi and +pi (called the principle argument)
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    1st quadrant: arg = arctan(y/x)
    2nd quadrant: arg = \pi - arctan(y/x)
    3rd quadrant: arg = -( \pi - arctan(y/x))
    4th quadrant: arg = -arctan(y/x)
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    Check the quadrant.
 
 
 
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