- Thread starter Yohib
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Please follow the rules of posting in this forum, as enunciated at:Prove that the focal radius of point on (a,b) of equation of parabola x^2=4ay is |a + b|

Please share your

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I suggest that the first thing you need to do is state exactly what "focal radius of a point" means.

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OP - have you managed to start this question? This is quite a nice page (click) if you're not familiar with a parabola's focus.

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Look at:Prove that the focal radius of point on (a,b) of equation of parabola x^2=4ay is |a + b|

https://math.stackexchange.com/questions/279457/how-to-find-focal-radius-in-parabola

for a definition and equation for focal radius.

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@Dr.Peterson I treated "a" as a constant within the equation. And for a certain value of "a" you obtain a single point (a,b) where "b" can be expressed in terms of a (this helps with the proof).

The second link in post#4 almost shows the identical equation to the question, and it states where the focus is. Given this, the rest is actually easy.

(Before I found this link I'd worked out the location of the focus "the hard way" by using angle of incidence=angle of reflection. I guess this is what most people would do in an exam since I'm guessing that not many people would have the parabola focus position memorised.)