xy plane

CITI29 · Posted: Sat Jul 26, 2008 5:43 pm Post subject: xy plane

In the xy plane, point (r,s) lies on the circle with the centre at the origin. What is the value of r^2 +s^2?

1. The circle has radius 2
2. The point (v2,-v2) lies on the circle

ans 'd'

augusto · Posted: Sun Jul 27, 2008 1:04 am Post subject:

Hi CITI,

To understand this problem I imagine that the point (r,s) is a vertice in a triangle. So that triangle has one side of lenght *r* another side of length *s* and the lenght of the hypotenuse equal to the radius of the circle.

So if you can imagine that, then r^2 + s^2 is one of the "sides" of the pythagoras theorem. So this is asking the value of the square of the radius.

So from (1) you know that the answer is 2^2 which is enough.
From (2) you can get the value of the radius, because you know that the circle is centered in the origin.

*note*: Just in case I'm assuming that the 'v's in (v2,-v2) are typos, and that the point is (2,-2)... which funny enough gives a different result both answers...

CITI29 · Posted: Sun Jul 27, 2008 7:28 am Post subject:

Hi augusto,

Thanks for thr reply. No, there's no typo in second sentence!. It is as it says.

augusto · Posted: Sun Jul 27, 2008 10:46 am Post subject:

Upz,

Well, please tell me if you know what those 'v's stand for.

Thanks,
augusto