During a trip to a fo
9- dzyurbw3  fh8l8s(orest to forage for mushrooms, Viviane finds a giant mushroom. She decides to model the shape of the mushroom to find 
ulb8 oyw fsr -hzd839(its volume.
 
After taking a photo of the mushroom and zooming in to get its real size, she rotates the photograph and estimates that the cross-section passes through the points  (0,3)   (15,3),(15,15),(22,10),(23.5,6)  and  (24,0) , where all measurements are in centimetres. The cross-section is symmetrical about the  x -axis, as shown below.
 
Viviane models the section from  (0,3)  and  (15,3)  with a straight line.
1. Write down the equation of the line that passes through these points.
y= 
 .
Next, Viviane models the section that passes through the points  (15,15),(22,10) ,  (23.5,6)  and  (24,0)  with a quadratic curve. it is ( 
 , 
 )
2. 1. Use your G.D.C. to find the equation of this quadratic curve.
y≈-1.82(x-a)$^2$+a;a= 
 .
2. By considering the gradient of the curve at the point  (15,15) , explain why this may not be a good model.
Viviane thinks she can obtain a better model if a quadratic passing through the point  (24,0)  with a maximum point at  (15,15)  is used.
3. Find the equation of this model, in the form  y=a(x-h)^{2}+k .
Using this new model, Viviane proceeds to estimate the volume of the mushroom by finding the volume of revolution about the  x -axis.
4. 1. Write down an expression for her estimate as a sum of two integrals.
2. Find the volume of the mushroom estimated by Viviane.
V≈ 
  cm$^2$ (round number)