Homework Help: Math

Posted by Joshua on Friday, October 17, 2008 at 6:41am.

Hi guys,
In the question "It is given that P (0, 3), Q(7, 5), R(9, -2) and S are vertices of a square. A circle A passes through the points P, Q, R and S. Find the equation of this circle. Hence or otherwise find the equation of circle B which is the image of A under the reflection about y – axis."

Can someone help me with the part hence or otherwise? I've found that the equation of the circle is x^2 + y^2 -9x -y -6 =0

Thanks =)

Math - drwls, Friday, October 17, 2008 at 9:06am
Assuming your answer is correct, it can be written

(x - 9/2)^2 + (y - 1/2)^2 = 106/4

(check my numbers)

The reflection about the y axis would be

(x + 9/2)^2 + (y - 1/2)^2 = 106/4
Math - Joshua, Friday, October 17, 2008 at 9:40am
Hi drwls,
Just wondering, does the word "under" in the question influence the question at all?

Thanks for your reply! =)
Math - drwls, Friday, October 17, 2008 at 10:53am
In this mathematics context, "Under the reflection about (an axis)" is the same as saying "after a reflection about (an axis)"

Mathematicions often us the preposition "under" to indicate carrying out an operation. It does not mean "below" in this case.
Math - Joshua, Friday, October 17, 2008 at 10:57am
Thanks drwls for the good explanation =)

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