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C3 functions

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1. http://www.examsolutions.net/a-level...e/paper.php#Q4
for part d i only got

what did i do wrong?
i subbed the largest and smallest numbers of the domain into g(x)

Edit: oops sign is wrong way
2. (Original post by bigdonger)
http://www.examsolutions.net/a-level...e/paper.php#Q4
for part d i only got

what did i do wrong?
i subbed the largest and smallest numbers of the domain into g(x)
Because by substituting x=0, you've only calculated where the graph touches the y axis. The function is a quadratic, so it has a minimum point; this minimum point is where y is smallest.

Find dy/dx of the curve and equate it to zero, giving you an x value which you can then substitute back into your function equation.
Alternatively, you could put your function in the 'completing the square' form and read off the coordinates. You know that this y coordinate is the minimum of y.
3. (Original post by JLegion)
Because by substituting x=0, you've only calculated where the graph touches the y axis. The function is a quadratic, so it has a minimum point; this minimum point is where y is smallest.

Find dy/dx of the curve and equate it to zero, giving you an x value which you can then substitute back into your function equation.
Alternatively, you could put your function in the 'completing the square' form and read off the coordinates. You know that this y coordinate is the minimum of y.
thanks

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