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# Bit confused on this... watch

1. Hey, I was just confused on how to actually do these two questions.
I did number 7a (I got 3x^2 + 12x +12) but not the other three. I would appreciate some help. Thanks! 😀

2. (Original post by homeland.lsw)
Hey, I was just confused on how to actually do these two questions.
I did number 7a (I got 3x^2 + 12x +12) but not the other three. I would appreciate some help. Thanks! 😀

Lovely work on part(a), it's all correct!

For part(b) you know that stationary points are solutions to the equation , can you solve this equation and find the x-coordinates of the stationary points?
3. (Original post by Zacken)
Lovely work on part(a), it's all correct!

For part(b) you know that stationary points are solutions to the equation , can you solve this equation and find the x-coordinates of the stationary points?
So would I factorise the answer to part a to get 3(x+2)(x+2) and then solve for x?
4. (Original post by homeland.lsw)
Hey, I was just confused on how to actually do these two questions.
I did number 7a (I got 3x^2 + 12x +12) but not the other three. I would appreciate some help. Thanks! 😀

For 7.b., you need to remember the important fact that at stationary points and that at maxima (i.e. there is downwards curvature, the gradient is decreasing) and at minima (i.e. there is upwards curvature, the gradient is increasing).

This should help you answer question 8.b. too. For 8.c, think about the shape of inflection points - how might you show it's an inflection point? Hint: you may want to use .
5. (Original post by homeland.lsw)
Hey, I was just confused on how to actually do these two questions.
I did number 7a (I got 3x^2 + 12x +12) but not the other three. I would appreciate some help. Thanks! 😀

For 7b) Derive the equation again, as it is a stationary point d2y/dx2 must =0, rearrange for x and sub it back into the orignal equation to get they y coordinate
6. (Original post by homeland.lsw)
So would I factorise the answer to part a to get 3(x+2)(x+2) and then solve for x?
Yes, that's correct. Once you've found the requisite values of you then need to check whether is positive, negative or zero for each of the x's that you've found to categorise it as a minimum, maximum or inflection.
7. (Original post by K-Fox)
For 7b) Derive the equation again,
Do you mean differentiate?
8. (Original post by Zacken)
Yes, that's correct. Once you've found the requisite values of you then need to check whether is positive, negative or zero for each of the x's that you've found to categorise it as a minimum, maximum or inflection.
Ok great, so my answer is this...
Attachment 511841511843511900

Also what's the story with that ?It's a bit confusing...

Edit I don't know why there are three attachments
Attached Images

9. (Original post by homeland.lsw)
Ok great, so my answer is this...
Attachment 511841511843511900

Also what's the story with that ?It's a bit confusing...

Edit I don't know why there are three attachments
have you seen this before? It's the derivative of the derivative.
10. (Original post by Zacken)
have you seen this before? It's the derivative of the derivative.
I haven't no...we covered maxima and minima using the method from question 7 and a table...

Anyway my question 7b is correct I presume? And I'll get on with question 8.
11. (Original post by homeland.lsw)
Ok great, so my answer is this...
Oh, and your stationary points is perfect. Good work! You just need to determine whether it's a minimum, maximum or inflection point now.

Once you find your second derivative (by differentiating your first derivative) you should get an equation that when you plug x=-2 in, it'll either give you a positive value (x=-2 is a minimum), a negative value (x=-2 is a maximum) or a zero (x=-2 is an inflection point).
12. (Original post by Zacken)
Oh, and your stationary points is perfect. Good work! You just need to determine whether it's a minimum, maximum or inflection point now.

Once you find your second derivative (by differentiating your first derivative) you should get an equation that when you plug x=-2 in, it'll either give you a positive value (x=-2 is a minimum), a negative value (x=-2 is a maximum) or a zero (x=-2 is an inflection point).
And if by magic it gave me zero!!!

Also you remind me of my maths teacher by saying "plug in"
13. (Original post by homeland.lsw)
And if by magic it gave me zero!!!

Also you remind me of my maths teacher by saying "plug in"
Yeees! Inflection it is. I get the same thing.

I really should be saying "substitute" instead of "plug in".
14. (Original post by Zacken)
Yeees! Inflection it is. I get the same thing.

I really should be saying "substitute" instead of "plug in".
Ok so this is my number 8...

Attachment 511857511859
Attached Images

15. (Original post by homeland.lsw)
Ok so this is my number 8...
Attachment 511857511859
All correct.
16. (Original post by Zacken)
All correct.
I'm practically a mathematician now!!
17. (Original post by homeland.lsw)
I'm practically a mathematician now!!
I concur.
18. (Original post by longshot100)
...
19. (Original post by Zacken)
Oh lol, sorry

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