## Example

A ball has been thrown upwards. It;s height at time**t**seconds can be given by the following formula.

h = 35t – 5t

Find the maximum height it reaches.
If you’re to sketch the problem on a graph you would get something like this.
That is the ball goes up in the air until it reaches a maximum point and then falls to the ground.
From learning stationary points you know that stationary points can be found where the gradient ^{2}**f ‘ (x)**is equal to zero as expressed here: This means we have to differentiate the given equation above. where

**f ‘ (x)**is equal to zero. …now we know at

**t = 3.5**we have a stationary point when

**t = 3.5**the height is: This gives us the maximum height it reaches at

**61.25**You can actually check whether it’s the maximum as shown below. we know that when: the point is at a maximum height.

## Example 2

Farmer John wants to make a pen for his sheep. What is the largest are of the largest rectangular pen he can make? It might be a good idea yo illustrate the problem in otherwise draw the rectangular pen he’s after. The rectangle is shown below. I have named the sides x and y. We know that the formula to find the area is**A =x x y**We have the perimeter as the given value; 1200m . We need to get reed of one of the letters in our area formula. Make all the letters in the equation the same. The perimeter formula is

**P = 2x + 2y**This can be expressed as below since we have the perimeter value;

2x + 2y = 1200

Simplify…
x + y = 600

this means…
y = 600 – x

If we substitute this into the formula to find the area it becomes.
A = x(600 – x)

A = 600x – x

using the stationary points calculations the largest rectangular pen can be found where…
Now use the x value in the area formula to find the required area…
The area of the largest rectangular pen that farmer John can make is 90,0000m^{2}^{2}You can check this as the in the following; when the point is a maximum so our area is correct.