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A rectangular pen is to be built with 1200 m of fencing. The pen is to be divided into three parts using two parallel partitions.

A) Find the maximum possible area of the pen. (45000 m^2)

B) explain how the maximum area would change if each side of the pen had to be at least 180 m long.

2) Relevant Equations

A=lw

3) Attempt at solution

A=lw

=(1200-2w)w

=1200w-2w^2

dA/dw=1200-4w

0=1200-4w

w=300

l=600

A=(600)(300)

=180000 m^2

This was the method I was taught to solve this question. I don't understand how the answer is 45000 m^2.

b) 0>_w>_180

Solve for w at both 0 and 180

0>_l>_180

Solve for l at both 0 and 180

Find area using a=lw

Once again incorrect answer by myself. What am I doing wrong? Am I missing something?