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# Don't understand the answers? Min and Max points *urgent watch

1. The question is: for the following curve find any stationary points and determine whether they are maximum or minimum:
y= 5x^2(x-6)

(-2, -160) and (2, -80)
but the answers are (4, -160) and (0,0)?

I have got all of the other questions in this exercise right so I don't understand the difference of this one?
It is in the core maths 1 and 2 heinemann book exercise 11A, Q 4B
2. You need to differentiate the equation using...
3. (Original post by jazz_xox_)
The question is: for the following curve find any stationary points and determine whether they are maximum or minimum:
y= 5x^2(x-6)

(-2, -160) and (2, -80)
but the answers are (4, -160) and (0,0)?

I have got all of the other questions in this exercise right so I don't understand the difference of this one?
It is in the core maths 1 and 2 heinemann book exercise 11A, Q 4B
Yeah so that means you got it wrong. Check it again.
4. (Original post by RDKGames)
Yeah so that means you got it wrong. Check it again.
Can you identify two different functions..
5. (Original post by ithinkitslily)
ok so you start off by expanding the equation:

y = 5x2(x - 6)
= 5x3 - 30x2

we can this differentiate this into:

dy/dx = 15x2 - 60x

at stationary points, the gradient is 0 so we can equate that equation to 0 and factorise:

15x2 - 60x = 0
15x (x - 4) = 0

therefore, by equating each side to 0, we know x = 4, x = 0 (0/15 = 0)

finally, you can substitute those values back into the original equation to find the y coordinate, giving you (4,-160) and (0,0) and work out what type of point they are
Yeah this is right but I don't think we are allowed to type up full solutions on TSR.
6. (Original post by Dynamic_Vicz)
Yeah this is right but I don't think we are allowed to type up full solutions on TSR.
ummm what why
7. (Original post by jazz_xox_)
The question is: for the following curve find any stationary points and determine whether they are maximum or minimum:
y= 5x^2(x-6)

(-2, -160) and (2, -80)
but the answers are (4, -160) and (0,0)?

I have got all of the other questions in this exercise right so I don't understand the difference of this one?
It is in the core maths 1 and 2 heinemann book exercise 11A, Q 4B
Is this by any chance a C3 question?
8. (Original post by Dynamic_Vicz)
Can you identify two different functions..
What two different functions....? If you're talking about the product then yes I can, what's your point?
9. (Original post by Dynamic_Vicz)
Is this by any chance a C3 question?
p sure its c1
10. to decide if it is a max or min you put the x value into the second derivative. if it comes out negative there is a max, if it is positive it is a min.
11. (Original post by ithinkitslily)
ummm what why
Because that's what it says on the "Posting Guide - Please Read!" thread in red font at the very top of this forum which is hard to miss.

http://www.thestudentroom.co.uk/show...9#post64637319
12. (Original post by RDKGames)
Because that's what it says on the "Posting Guide - Please Read!" thread in red font at the very top of this forum which is hard to miss.

http://www.thestudentroom.co.uk/show...9#post64637319
oooh gotta stay in line w the precious posting laws 😩
13. (Original post by Dynamic_Vicz)
Is this by any chance a C3 question?
It's C1
14. (Original post by ithinkitslily)
ok so you start off by expanding the equation:

y = 5x2(x - 6)
= 5x3 - 30x2

we can this differentiate this into:

dy/dx = 15x2 - 60x

at stationary points, the gradient is 0 so we can equate that equation to 0 and factorise:

15x2 - 60x = 0
15x (x - 4) = 0

therefore, by equating each side to 0, we know x = 4, x = 0 (0/15 = 0)

finally, you can substitute those values back into the original equation to find the y coordinate, giving you (4,-160) and (0,0) and work out what type of point they are
Ah, thank you! The mistake I made was writing the x value as a constant so I factorised it into 2 brackets makes sense now, thanks!
15. (Original post by ithinkitslily)
ummm what why
This is the thread explaining why - http://www.thestudentroom.co.uk/show...9#post64637319

(Original post by RDKGames)
What two different functions....? If you're talking about the product then yes I can, what's your point?
OP could've differentiated Y using the product rule. However I guess this technique is a bit sophisticated for the question.

(Original post by jazz_xox_)
It's C1
Oh alright. I'm an A2 Maths student so I approached the question using a C3 technique.
16. (Original post by ithinkitslily)
oooh gotta stay in line w the precious posting laws 😩
There's good reason for it: if you post hints and tips along the line of "try this next and see where you get", then you're helping the poster develop their skills. They'll then be able to do the next question they come across, they'll ace their exams, then they'll succeed in life, and become world famous millionaires.

On the other hand, if you post full solutions you may get someone out of an immediate homework bind, but they will learn little, will fail their exams, and will be condemned to a life of penury.
17. (Original post by Gregorius)
There's good reason for it: if you post hints and tips along the line of "try this next and see where you get", then you're helping the poster develop their skills. They'll then be able to do the next question they come across, they'll ace their exams, then they'll succeed in life, and become world famous millionaires.

On the other hand, if you post full solutions you may get someone out of an immediate homework bind, but they will learn little, will fail their exams, and will be condemned to a life of penury.
Oh no, the life of penury isn't for me I do now understand the question ... world famous millionaire?

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