anonymous
  • anonymous
The image of a point after a –90° rotation about the origin is (–4, 7). What are the coordinates of the preimage?
Mathematics
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SOLVED
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chestercat
  • chestercat
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anonymous
  • anonymous
Im not sure what branch of maths your working with but i would be inclined to use the fact that multiplying a complex coordinate by i gives a 90degree anticlockwise rotation. so make (-4,7) -4+7i and work with that ?
anonymous
  • anonymous
\[x=x'\cos(\theta)+y'\sin(\theta)\]\[y=-x'\sin(\theta)+y'\cos(\theta)\]Where\[x'=-4|y'=7|\theta=-90\]
anonymous
  • anonymous
that is a much better way of doing things

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anonymous
  • anonymous
@Taplin44, I do not know these equations by heart, I derive them from the same approach you have declared, multiplication of complex numbers
anonymous
  • anonymous
Good to know, Your equations are much more applicable to someone who doesnt know the topic if that is the case though.
amistre64
  • amistre64
one way to assess it is to draw out a general setup |dw:1377694941316:dw|

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