SOLUTION: A rectangle has one corner on the graph of y=36-x^2 another at the origin a 3rd on the positive y-axis, and the fourth on the positive x-axis. Express the area A of the rectangle a

Algebra ->  Functions -> SOLUTION: A rectangle has one corner on the graph of y=36-x^2 another at the origin a 3rd on the positive y-axis, and the fourth on the positive x-axis. Express the area A of the rectangle a      Log On


   



Question 854501: A rectangle has one corner on the graph of y=36-x^2 another at the origin a 3rd on the positive y-axis, and the fourth on the positive x-axis. Express the area A of the rectangle as a function of x. What is the domain of A? For what value of x is A largest?
ANY HELP WOULD BE SOOOO WELCOME!! Thanks in advance I am super confused!

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
It's a good 1st step to draw the parabola
and also a horizontal line which represents
both the point on the y-axis ( 0, y ) and
also the intersection of this line with the
parabola ( x, y ).
Remember that the horizontal line can be
ANY horizontal line
-------------------------------------
+graph%28+400%2C+400%2C+-10%2C+10%2C+-10%2C+40%2C+24%2C+-x%5E2+%2B+36+%29+
So far, I have the points:
( 0, 0 )
( 0, y )
( x, y )
Now I can add the final point ( x1, 0 )
Both x and y are positive
---------------------------------
+A+=+x%2Ay+
+A+=+x%2A%28+-x%5E2+%2B+36+%29+
+A+=+-x%5E3+%2B+36x+
I can plot this on top of the previous plot

The domain is +0+ to +6+
----------------------------
Are you in a calculus class? That's the only way I know to
find the peak of 3rd degree equation
+A+=+-x%5E3+%2B+36x+
+A%27+=+-3x%5E2+%2B+36+
+A%27+=+0+ ( slope = 0 )
+-3x%5E2+%2B+36+=+0+
+3x%5E2+=+36+
+x%5E2+=+12+
+x%5Bmax%5D+=+2%2Asqrt%283%29+
This is the value of x for which +A+ is largest
----------------------------
and now find +y%5Bmax%5D+
+y%5Bmax%5D+=+-x%5E2+%2B+36+
+y%5Bmax%5D+=+-%28+2%2Asqrt%283%29+%29%5E2+%2B+36+
+y%5Bmax%5D+=+-4%2A3+%2B+36+
+y%5Bmax%5D+=+36+-+12+
+y%5Bmax%5D+=+24+
-----------------
Hope this all makes sense- if you do it with a
non-calculus method, you should get the
same answer