Boy Mow Chau's answer to Candice lim's Junior College 1 H2 Maths Singapore question.
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As mentioned before, make a sketch of the points to better visualise the problem.
Date Posted:
2 years ago
Thanks alot ! Mr Chau.
Really appreciate your advice and working solution :)
Really appreciate your advice and working solution :)
missed something ...
the question says prove that tangents can be drawn, and gives the condition a.b > 0.
so need to add comment ...
a.b > 0
=> cos(AOB) > 0
=> AOB < 90 degrees
=> point O must lie outside the sphere
=> tangents can be drawn.
if a.b < 0,
then O must lie inside the sphere,
so cannot have any tangents from O.
the question says prove that tangents can be drawn, and gives the condition a.b > 0.
so need to add comment ...
a.b > 0
=> cos(AOB) > 0
=> AOB < 90 degrees
=> point O must lie outside the sphere
=> tangents can be drawn.
if a.b < 0,
then O must lie inside the sphere,
so cannot have any tangents from O.
ah...i see. Noted with thanks Mr Chau.
Have a early rest. Thanks again and good night :)
Have a early rest. Thanks again and good night :)
Hi Mr Chau, sorry to trouble you but may I know what does cone formed by all tangents from O to S meet S in a circle of radius r mean? Appreciate your advice. Thanks!
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