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April 20, 2014

Posted by **Gigi** on Monday, July 23, 2012 at 10:08am.

1) x^2-y^2=4 (You may leave your answer for this one as r2 =)

2) x^2+(y-1)^2=1

- math -
**Reiny**, Monday, July 23, 2012 at 10:33amwe know

r^2 = x^2 + y^2

x/r = cosØ, and y/r = sinØ or x=rcosØ and y = rsinØ

x^2 - y^2 = 4

r^2 cos^2 Ø - r^2 sin^2Ø = 4

r^2 (cos^2 Ø - sin^2 Ø) = 4

r^2 (cos 2Ø)=4

r^2 = 4/cos 2Ø or r^2 = 4sec 2Ø

follow the same procedure for the second one, let me know what you got

- math -
**Gigi**, Monday, July 23, 2012 at 10:53amhow did you get cos 2Ø after subtracting cos^2Ø-sin^2Ø?

- math -
**Reiny**, Monday, July 23, 2012 at 1:08pmOne of the basic trig identities says:

cos 2A = cos^2 A - sin^2 A

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