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# A-Level C1 differentiation question watch

1. Given that

y = 2x^(3/2) - 1,

Show that

4x^2((d^2)y/dx^2) - 3y = k

Heres an image:

2. (Original post by Tobiq)
Given that

y = 2x^(3/2) - 1,

Show that

4x^2((d^2)y/dx^2) - 3y = k

Heres an image:

What have you tried?
3. (Original post by SeanFM)
What have you tried?
Literally no help whatsoever....
4. (Original post by SeanFM)
What have you tried?
5. (Original post by Tobiq)
Literally no help whatsoever....
Calculate the second derivative, plug everyth into the left hand side of the equation and find out what k is. Unless you show some sign of trying that, there's not much point just telling you the answer.
6. (Original post by Tobiq)
Literally no help whatsoever....
I'm sorry. good luck with your question
7. This is not a C1 question, at least not for me as it involves a double derivative.
8. (Original post by nwmyname)
This is not a C1 question, at least not for me as it involves a double derivative.
It's from a solomon paper.
9. Do the d2y/dx2 on the first equation and then subsitute it into the second equation to find a value for k.
Not that hard tho.
10. (Original post by Tobiq)
Given that

y = 2x^(3/2) - 1,

Show that

4x^2((d^2)y/dx^2) - 3y = k

Heres an image:

You've found an equation for from part a of the question, and you know the equation of y to be so you can simply plug them in to the equation given to find the value of k
11. (Original post by nwmyname)
Do the d2y/dx2 on the first equation and then subsitute it into the second equation to find a value for k.
Not that hard tho.
1. Theres only 1 equation given... what are you talking about?
2. Where does the value of K come from? what does it even represent.
12. (Original post by Tobiq)
1. Theres only 1 equation given... what are you talking about?
2. Where does the value of K come from? what does it even represent.
k is something you are going to find.

The first equation right at the top?
13. (Original post by Tobiq)
1. Theres only 1 equation given... what are you talking about?
2. Where does the value of K come from? what does it even represent.
In a "show" question you have to arrive at whats given... you cant use it in the solution
14. (Original post by Tobiq)
In a "show" question you have to arrive at whats given... you cant use it in the solution
Yes, you show that when you subsitute dy2/dx2, you get a value that is a constant.
A constant being an integer value, e.g. 1 or 2 or 3 or 4.
15. (a) dy/dx= 3x^0.5
d^2y/dx^2=3/2x^-.05
(b) 4x^2(3/2x^-0.5)-3y
6x^3/2-3y=k
3y=6x^3/2-k
y=2x^3/2-1/3k
k=3
16. (Original post by nwmyname)
Yes, you show that when you subsitute dy2/dx2, you get a value that is a constant.
A constant being an integer value, e.g. 1 or 2 or 3 or 4.
I've had y'' . What is done next, the only other information given is y=2x^(3/2) - 1;

How do i use y, and y'' to arrive at the equation wielding the K
17. (Original post by Tobiq)
I've had y'' . What is done next, the only other information given is y=2x^(3/2) - 1;

How do i use y, and y'' to arrive at the equation wielding the K
Once you differentiate y into dy/dx, you differentiate it again to dy2/dx2.

Then substitute the value that you get.
18. (Original post by Tobiq)
Ok, so you have and y =

The question is, what is the value of ? Because you'll note that the terms involving x are going to cancel out.
19. (Original post by Tobiq)
I've had y'' . What is done next, the only other information given is y=2x^(3/2) - 1;

How do i use y, and y'' to arrive at the equation wielding the K
Just substitute y" into the d^2y/dx^2 bit of the k equation, and then simplify it out.

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