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Here is a link to the question:I need help on a HW problem - I got the first two parts right, but am having trouble finishing the last two?I need help on a HW problem - I got the first two parts right, but am having trouble finishing the last two parts.

The figure shows a sector with radius r and angle θ in radians. The total perimeter of the sector is 120 cm.

(a) Express θ as a function of r.

I got

Theta = 2r-120/-r

(b) Express the area of the sector as a function of r.

I got A=1/2 * r^2 * (2r-120/-r)

Now these are the two that I am having trouble figuring out.

(c) For what radius r is the area a maximum?

in cm

and

(d) What is the maximum area?

in cm^2

I have to answer them as exact answers - no decimals allowed. Is there anyone who would be willing to walk me through this?

Thanks.

I need help on a HW problem - I got the first two parts right, but am having trouble finishing the last two? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.