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Locus

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Nialllovespie:
How do I solve this problem:

Find the equation of the locus of a point that moves so that its distance from the line 3x+4y+5=0 is always 4 units.

The answer is 3x+4y-15=0, 3x+4y+25=0 (if that's any help) but I have no idea how to solve it.

Thank you so much for your help!!

RuiAce:

--- Quote from: Nialllovespie on October 11, 2016, 05:10:34 pm ---How do I solve this problem:

Find the equation of the locus of a point that moves so that its distance from the line 3x+4y+5=0 is always 4 units.

The answer is 3x+4y-15=0, 3x+4y+25=0 (if that's any help) but I have no idea how to solve it.

Thank you so much for your help!!

--- End quote ---



________________________

pels:
So when do you know when to use distance formula or perpendicular distance formula for locus questions

Also, for the one you mentioned:

P moves so that it is 2 units away from (4,2), is it just a circle with centre (4,2) radius 2?

Is that correct? :P

RuiAce:
Yeah that easy one becomes a circle.

You always tend to the distance formula if you can. The perpendicular distance formula should NEVER be the number 1 option; it is an alternative.

Note that perpendicular distance demands that a line be present. Without a line, you can't even use it.

pels:
Yeah thought so.

Cheers Rui

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