# Area of frame

• Mar 26th 2010, 01:19 AM
mastermin346
Area of frame
Diagram 5 shows a wire frame.The length of the wire is 60 cm and the radius of the semicircle is $\displaystyle r cm$

(i)show that the area of the frame,$\displaystyle L cm^2,$ is given by $\displaystyle L=60r-2r^2-\frac{1}{2}\pi r^2$

(ii)Hence,calculate the maximum area of the frame
• Mar 26th 2010, 01:41 AM
sa-ri-ga-ma
Length of the wire l = 2h + 2r + πr.
From the above equation, find the expression for h.
The area of frame L = h*2r + 1/2*π*r^2.
Substitute for h and find L.
For maximum area, find dL/dr and equate it to zero. Hence find r.
• Mar 27th 2010, 08:48 AM
mastermin346
can anyone teach me with the step to get the answer please.
• Mar 27th 2010, 09:09 AM
sa-ri-ga-ma
Quote:

Originally Posted by mastermin346
can anyone teach me with the step to get the answer please.

In this forum we will give the hint. If you want to learn the subject you have to the calculations yourself.
In the problem length of the wire l = 60 cm is given. Substitute this value in the first equation, rearrange the terms so that the equation should be
h = .............?
• Mar 29th 2010, 07:45 PM
sa-ri-ga-ma
Still you are not showing your calculations.