My Math Forum Perimeter of a Sector

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 March 13th, 2013, 09:51 AM #1 Senior Member   Joined: Sep 2011 Posts: 395 Thanks: 0 Perimeter of a Sector Just a quick question, here. I think the books final answer may be incorrect, but can anyone help me confirm if that is the case. Many thanks. Q. The perimeter of a sector of a circle of radius r is 8 cm. Express $\theta$ in terms of r , where $\theta$ is the angle of the sector in radians. Attempt: Perimeter of a circle: $2r+\theta r=2r+2\pi r$ $2r+2\pi r=8$ $2\pi r=8-2r$ $\theta=\frac{8-2r}{r}$ $\theta=\frac{8}{r}-2$ Answer: (From text book): $\frac{8}{r}-r$
 March 13th, 2013, 10:13 AM #2 Math Team   Joined: Nov 2010 From: Greece, Thessaloniki Posts: 1,990 Thanks: 133 Math Focus: pre pre pre pre pre pre pre pre pre pre pre pre calculus Re: Perimeter of a Sector [color=#000000]I get the same result, $\text{Perimeter}=\text{arc length}+2r=\theta\cdot r+2r\Rightarrow \left(\theta+2\right)r=8\Rightarrow \theta=\frac{8}{r}-2$.[/color]
 March 13th, 2013, 10:30 AM #3 Senior Member   Joined: Sep 2011 Posts: 395 Thanks: 0 Re: Perimeter of a Sector Thanks for checking that.

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