A curve has the equation , where .
- (a)
Find .
- (b)
Find the exact value of the coordinates of the stationary point.
- (c)
Determine the nature of the stationary point.
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Worked solution
3(a)
1. Apply the quotient rule to differentiate the function
Let and .
Then and .
Using the quotient rule :
2. Simplify the derivative
3(b)
1. Set the derivative from part (a) to zero to find the stationary point
From part (a), .
For a stationary point, .
2. Solve for the $x$-coordinate of the stationary point
Since for all , we have:
3. Find the corresponding exact $y$-coordinate
Substitute into the original equation:
The coordinates are .
3(c)
1. Use the first derivative test to check the sign of the gradient around the stationary point $x = 2.5$.
From earlier parts, and the stationary point is at .
For slightly less than (e.g., ):
, , and , so .
For slightly greater than (e.g., ):
, , and , so .
2. Conclude the nature of the stationary point.
Since the gradient changes from negative to positive as increases through , the stationary point is a minimum point.
Minimum point
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