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Question

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iwanttogotostanford · Answer

@3mar

sunnnystrong · Answer

Okay... so recall that:

$$f(x)=x^2$$

than
$$f'(x)=2x$$

sunnnystrong · Answer

This is a graph of a parabola shifted up 9 units and reflected across the x-axis

sunnnystrong · Answer

so:
$$f(x)= -x^2+9$$
$$f'(x)= -2x$$

sunnnystrong · Answer

What is f'(3)?

sunnnystrong · Answer

*approximately haha

3mar · Answer

It is a quadratic function with negative slope $-x^2$ symmetrical about the y-axis...

As it touches the x-axis at x=3 (3,0) and has a vertex at (0,9), so the base of the function would be: $f(x)=-x^2+9$


So easily its derivative could be gotten and then you can substitute with 3 in f'(x).


Can you @iwanttogotostanford???

iwanttogotostanford · Answer

@3mar i think D

3mar · Answer

No, the slope of the function at x=3 is not positive at all , , , Definitely
IT IS NEGATIVE as it is obvious from the figure

3mar · Answer

@sunnnystrong
what do you think sunny face!?

sunnnystrong · Answer

@3mar yep the derivative at x=3 is definitely negative there.

just think about what the slope of the tangent line is doing at x=3 ...|dw:1481175748469:dw|