area

[mr.burger]

What is the maximum area of a rectangle whose base lies on the x-axis and whose other two vertices lie on the graph of y= -x^(2) +4?

 

[Gene]

the graph is symetrical about the y axis and is a downward opening parabola. If one point is (-a,y) the other top point is (a,y) and the area is
A = 2a*y = 2a*(-a^2+4) = -2a^3+8a
Find dA/da = 0