Preliminary QAT 2008 (1 Viewer)

[totallybord]

Hi,

Just wanted to clarify and get someone to double check whether I am right or not.

QAT 2008 Preliminary course paper - I cannot seem to find it again but I have printed it out =/

There is a graph f'(x)

The question is write down the value of x for which y=f(x) is increasing. I would say that it would be x<2 and 2<x<4
but somehow the answer says x>4 and x<2?

Why
what am i missing

 

[pikachu975]

This is a gradient graph. When it is above the x axis, the gradient is positive. Therefore increasing from 2 to 4.

 

[He-Mann]

This is a gradient graph. When it is above the x axis, the gradient is positive. Therefore increasing from 2 to 4.

By your (correct) reasoning, your conclusion should be x < 4 (x =/= 2).

Not sure why the answer said x > 4 because those yield a negative gradient. i.e. decreasing.

 

[Lugia101101]

I know that all of the teachers for maths I've had in the past have said that the markers for the HSC don't care whether you include the roots of the derivative function. Although, in this case, because the graph meets the axis, being a stationary point, I imagine they'd want x < 2, 2 < x < 4.

 

[He-Mann]

I know that all of the teachers for maths I've had in the past have said that the markers for the HSC don't care whether you include the roots of the derivative function. Although, in this case, because the graph meets the axis, being a stationary point, I imagine they'd want x < 2, 2 < x < 4.

Why would you neglect the interval of 2 < x < 4 which shows that the curve is increasing?

 

[Lugia101101]

You don't, the answer is x < 2, 2 < x < 4.