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Core 1 (Edexcel)

For what value of n is X the smallest
x=(n-5)^2 +2
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Avatar for tehforum
tehforum
20
5?
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Avatar for raheem94
raheem94
13
Original post by reb0xx
For what value of n is X the smallest
x=(n-5)^2 +2


Differentiate the expression with respect to n, and set the derivative equal to zero.

Or you can also just notice the value by looking at the equation.

By the way, why is the thread label undergraduate?
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Avatar for reb0xx
reb0xx
OP
2
Original post by raheem94
Differentiate the expression with respect to n, and set the derivative equal to zero.

Or you can also just notice the value by looking at the equation.

By the way, why is the thread label undergraduate?


Ok thank you but what if there are two values of 0
from maximun and minimum
Reply 4
Avatar for raheem94
raheem94
13
Original post by reb0xx
Ok thank you but what if there are two values of 0
from maximun and minimum


I am not understanding your question.

You differentiate, and set the derivative equal to zero to find the values, then consider which value is max and which is min by finding the second derivative.
Original post by raheem94
I am not understanding your question.

You differentiate, and set the derivative equal to zero to find the values, then consider which value is max and which is min by finding the second derivative.


This question is clearly not meant for differentiation. Plus it'd be a lot more effort (at least for a Core 1 student as they'd need to multiply the bracket out then differentiate).



OP; you should have learnt how to find the minimum value (vertex) of a quadratic using completing the square. This is that.
Original post by Earnest Moore
n=(5+∞i)


2 posts and you're trolling -.-
Original post by hassi94
2 posts and you're trolling -.-


How is that trolling?

Please, point out if I made a mistake.
(edited 11 years ago)
Reply 8
Avatar for raheem94
raheem94
13
Original post by hassi94
This question is clearly not meant for differentiation. Plus it'd be a lot more effort (at least for a Core 1 student as they'd need to multiply the bracket out then differentiate).



OP; you should have learnt how to find the minimum value (vertex) of a quadratic using completing the square. This is that.


The thread label is 'undergraduate', so the OP should be knowing this mate. :biggrin:

I didn't understood what the OP was saying, so i recommended him to differentiate, the chapters may vary by boards, in edexcel i don't think they will give min max questions in C1, though i am not sure.

At this time of the year, the OP would have probably done C2 as well, so i think he might be knowing it.
Reply 9
Avatar for Aurum
Aurum
Original post by Earnest Moore
How is that trolling?

Please, point out if I made a mistake.


[br](n−5)2≥0[br](n−5)2+2≥2[br]x≥2[br](n-5)^2 \geq 0[br](n-5)^2 + 2 \geq 2[br]x \geq 2
Hence least value of x is 2, which occurs when n=5.
It's valid. No conditions were specified.

if;
[br]n∈R[br][br]n \in \mathbb{R}[br]
then fair enough, but that wasn't stated.
Reply 11
Avatar for nuodai
nuodai
17
For the sake of not confusing the OP, and to prevent the thread from descending into a flamewar, I've removed a few posts which went in this direction.

Original post by Earnest Moore
It's valid. No conditions were specified.

if;
[br]n∈R[br][br]n \in \mathbb{R}[br]
then fair enough, but that wasn't stated.


It says in the thread title that this is a C1 problem, so it didn't really need to be stated; and even if not, your post wasn't correct.
(edited 11 years ago)

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