Posted by **Tabby** on Friday, April 20, 2012 at 3:48pm.

i need to graph the polar equation

2 = r cos (theta + 180) on one of the graphs that looks like a flattened globe.

So far I have

2=r cos180 costheta + r sin180 sintheta

what do i do now?

- Polar equations - Help? -
**bobpursley**, Friday, April 20, 2012 at 4:03pm
Isn't cos(Theta+180)= -cosTheta ?

checking the hard way...

cos(A+B)=cosAcosB-sinAsinB

cos(Theta+180)= cosThetacos180-sinThetasin180= -cosTheta.

2= -rcosTheta

r= -2/cosTheta.

Graph it.

- Polar equations - Help? -
**Tabby**, Friday, April 20, 2012 at 4:12pm
thank you so much, I don't know how i missed that identity.

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