# Edexcel maths question

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#1
Pls can i get some help with part b
Last edited by Htx_x346; 1 month ago
0
1 month ago
#2
(Original post by Htx_x346)
Pls can i get some help with part b
Considering it's two marks you could just show what the two values give when used in the formula as you know what y value a should produce.
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1 month ago
#3
(Original post by Htx_x346)
Pls can i get some help with part b
Sub in y = 2, and x = 1.5 and 1.6. Should be a change of sign, so…

Josh Kelly.
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#4
(Original post by Skiwi)
Considering it's two marks you could just show what the two values give when used in the formula as you know what y value a should produce.
Thanks ill try that

Sub in y = 2, and x = 1.5 and 1.6. Should be a change of sign, so…

Josh Kelly.
Why would there be a change of sign since there isnt a root?
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1 month ago
#5
(Original post by Htx_x346)
Why would there be a change of sign since there isnt a root?
There isn’t a root as such, if there are solutions to f(x) = b, over a small interval, subbing in two values of x either side of the root would produce a change of sign of f(x) - b = 0, as long as the function is continuous.

Think back to what you have learnt in iteration

George Kambosos Jr.
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1 month ago
#6
(Original post by Htx_x346)
Why would there be a change of sign since there isnt a root?
But the question says ‘show there is a root’ so there is an assumed root.
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#7
There isn’t a root as such, if there are solutions to f(x) = b, over a small interval, subbing in two values of x either side of the root would produce a change of sign of f(x) - b = 0, as long as the function is continuous.

Think back to what you have learnt in iteration

George Kambosos Jr.
Oh yh i wasnt taught this topic

Still slightly confused about why it would produce a change of sign cause there isn’t a root, but ig ill just think about it
(Original post by User3858395)
But the question says ‘show there is a root’ so there is an assumed root.
It doesn’t say that?
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1 month ago
#8
My bad, for some reason I read that symbol as ‘root’. Maybe the sign change is down to a change in gradient. Best thing you can do at this stage is just learn and memorize how things are done. That’s what I do.
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1 month ago
#9
(Original post by Htx_x346)
Oh yh i wasnt taught this topic

Still slightly confused about why it would produce a change of sign cause there isn’t a root, but ig ill just think about it

It doesn’t say that?
You know the function is increasing in that part of the graph and
1.5^1.5 < 2 < 1.6^1.6
so ....
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#10
(Original post by mqb2766)
You know the function is increasing in that part of the graph and
1.5^1.5 < 2 < 1.6^1.6
so ....
That makes sense but what does it really mean?
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1 month ago
#11
(Original post by Htx_x346)
That makes sense but what does it really mean?
Why not use the iteration formula which you haven't copied.
0
1 month ago
#12
(Original post by Htx_x346)
That makes sense but what does it really mean?
It would probably be better for you to try and sketch whats happening.
* The function is increasing.
* You know (can evaluate) 1.5^1.5 < 2 < 1.6^1.6 or f(1.5) < f(x) < f(1.6)
So what can you conclude about the point where f(x)=2?
Last edited by mqb2766; 1 month ago
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#13
(Original post by mqb2766)
It would probably be better for you to try and sketch whats happening.
* The function is increasing.
* You know (can evaluate) 1.5^1.5 < 2 < 1.6^1.6 or f(1.5) < f(x) < f(1.6)
So what can you conclude about the point where f(x)=2?
Its between 1.5 and 1.6?
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1 month ago
#14
(Original post by Htx_x346)
Its between 1.5 and 1.6?
Of course. The first part asked you to find the location of hte minimum (1/e) and to the right of the minimum, the function is increasing. You use that knowledge in this part to show the function must be equal to 2 somewhere between 1.5 and 1.6.
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#15
(Original post by mqb2766)
Of course. The first part asked you to find the location of hte minimum (1/e) and to the right of the minimum, the function is increasing. You use that knowledge in this part to show the function must be equal to 2 somewhere between 1.5 and 1.6.
That makes sense but why is the change of sign relevant in this case?
Thank u
Last edited by Htx_x346; 1 month ago
0
1 month ago
#16
(Original post by Htx_x346)
That makes sense but why is the change of sign relevant in this case?
Thank u
Its similar to a root finding problem. Consider the function
g(x) = f(x)-2
as mentioned above. Then
g(1.5) < 0
g(1.6) > 0
so g() has a root somewhere between 1.5 and 1.6 which is the location where f()=2. Its the same argument.
Last edited by mqb2766; 1 month ago
0
#17
(Original post by mqb2766)
Its similar to a root finding problem. Consider the function
g(x) = f(x)-2
as mentioned above. Then
g(1.5) < 0
g(1.6) > 0
so g() has a root somewhere between 1.5 and 1.6 which is the location where f()=2. Its the same argument.
What does () mean
0
1 month ago
#18
(Original post by Htx_x346)
What does () mean
Its a function. Have you sketched what you think is happening - can you upload?
In general, your responses are very terse and it would help for your replies to contain more content about what you do undersetand ...
Last edited by mqb2766; 1 month ago
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