IGCSEsurvivor
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#1
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Can someone pls help me with section c
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mqb2766
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Couple of ways to approach it, but using the dot product = 0 is probably the easiest.
So D lies on the line and you want to determine the value of the line scalar multiplier which gives the dot product with the line direction as zero.
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IGCSEsurvivor
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why do we use the product rule?
(Original post by mqb2766)
Couple of ways to approach it, but using the dot product = 0 is probably the easiest.
So D lies on the line and you want to determine the value of the line scalar multiplier which gives the dot product with the line direction as zero.
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mqb2766
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Just imagine a line which does not pass through the origin.
All points a constant distance from the origin lie on a circle (distance r from the origin).
The closest point of a line is therefore when the circle expands just enough so that the line is a tangent to a point on the circle.
That point represents the closest point D and OD is perpendicular to the line direction (zero dot product).
(Original post by IGCSEsurvivor)
why do we use the product rule?
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IGCSEsurvivor
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I'm sorry I didn't quite get that :confused:
(Original post by mqb2766)
Just imagine a line which does not pass through the origin.
All points a constant distance from the origin lie on a circle (distance r from the origin).
The closest point of a line is therefore when the circle expands just enough so that the line is a tangent to a point on the circle.
That point represents the closest point D and OD is perpendicular to the line direction (zero dot product).
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mqb2766
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Which part? The diagram in
https://www.siyavula.com/read/maths/...al-geometry-03
is ok, with C = origin in your case.

The line has to be tangential to the circle which represents the distance from the origin and D is the tangent point.

(Original post by IGCSEsurvivor)
I'm sorry I didn't quite get that :confused:
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IGCSEsurvivor
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#7
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thanks I got it now
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