Question 125407
There are 3 sections of fence perpendicular to the river, each of
length {{{x}}}. Since the total amount of fencing is 360 yds, I have
{{{A = x*(360 - 3x)}}}
{{{x}}} is the width and {{{360 - 3x}}} is the length of 2 coralls
{{{A(x) = -3x^2 + 360x}}} answer
The domain is all values of {{{x}}} that make {{{A(x) >= 0}}}
{{{-3x^2 + 360x >= 0}}}
{{{3x*(-x + 120) >= 0}}}
The expression equals {{{0}}} when either 
{{{x = 0}}} 
OR
{{{-x + 120 = 0}}}
{{{x = 120}}}
There are 2 factors on the left side. The product is >0 when
either both are negative or both positive: (-)(-) or (+)(+)
{{{x < 0}}} AND {{{x > 120}}} (this is (-)(-))
OR
{{{x>0}}} AND {{{x < 120}}}
The first condition is impossible, since it requires {{{x}}} to be
negative and positive at the same time, so the domain is
{{{0 <= x <= 120}}}