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March 4, 2015

March 4, 2015

Posted by **Mary** on Tuesday, November 4, 2008 at 5:29pm.

- Math -
**Reiny**, Tuesday, November 4, 2008 at 6:32pmlet the point of contact in the first quadrant be (x,y)

then the base of the rectangle is 2x and its height is y

Area = 2xy

= 2x(9-x^2)

= 18x - 2x^2

d(area)/dx = 18 - 4x

so 18-4x=0

x = ....

take it from here, let me know what you got

- oops Math -
**Reiny**, Tuesday, November 4, 2008 at 6:50pmchange

<< = 18x - 2x^2 >> to

= 18x - 2x^3

then d(area)/dx = 18 - 6x^2

= 0 for a max/min of area

6x^2 = 18

x^2 = 3

x = ±√3

and y = 6

same result as Damon

- oops Math -
- Math -
**Damon**, Tuesday, November 4, 2008 at 6:38pmWell, this is an upside down parabola (sheds water) with x intercepts at x = -3 and x = +3 and vertex at (0,9)

so lets do it just for positive x and double the base at the end.

Area = x y

where y = 9-x^2

A = 9x - x^3

dA/dx = 9 - 3 x^2

that is zero when x^2 = 3

or x = +/- sqrt 3 use + sqrt 3

so y = 9 - 3 = 6

Now we double the base because we only did the right half

base = 2 sqrt 3

height = 6

- Math -
**brandon**, Tuesday, November 4, 2008 at 7:31pmhow do I write a written equation? A jacket cots 28.00 more than twice the cost of a pair of slacks. If the jacket costs 152.00, how much do th slacks cost?

- Math -

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