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Edexcel maths question

Pls can i get some help with part b538ABD8E-34C5-4143-B9FF-4FFF00D21C13.png
(edited 1 year ago)
Reply 1
Original post by Htx_x346
Pls can i get some help with part b538ABD8E-34C5-4143-B9FF-4FFF00D21C13.png

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.
Original post by Htx_x346
Pls can i get some help with part b538ABD8E-34C5-4143-B9FF-4FFF00D21C13.png


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

Josh Kelly.
Reply 3
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

Original post by Driving_Mad
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?
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.
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.
Reply 6
Original post by Driving_Mad
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?
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.
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 ....
Reply 9
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?
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.
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?
(edited 1 year ago)
Reply 12
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?
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.
Reply 14
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
(edited 1 year ago)
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.
(edited 1 year ago)
Reply 16
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
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 ...
(edited 1 year ago)

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