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Is this possible?

1. Homework Statement
If y'=0 and y=1 when x=2, and y''-4=0, find the function.


2. Homework Equations
[tex]\frac{dy}{dx}=\int\frac{d^{2}y}{dx^{2}}[/tex]



3. The Attempt at a Solution

I hate posting this because I am pretty sure the solution is easy but I just can't seem to see through this question...

If y'=0 then there must be no x term in the function f(x)... thus y=C is the only possibility. So then y=1 is the only possibility for the initial conditions given.... And if y''=4 then shouldn't y'=4x+C? :/
 

radou

Homework Helper
3,105
6
1. Homework Statement
If y'=0 and y=1 when x=2, and y''-4=0, find the function.


2. Homework Equations
[tex]\frac{dy}{dx}=\int\frac{d^{2}y}{dx^{2}}[/tex]



3. The Attempt at a Solution

I hate posting this because I am pretty sure the solution is easy but I just can't seem to see through this question...

If y'=0 then there must be no x term in the function f(x)... thus y=C is the only possibility. So then y=1 is the only possibility for the initial conditions given.... And if y''=4 then shouldn't y'=4x+C? :/
The boundary values are y(2) = 1 and..? What do you mean by y' = 0? For which x is this true?
 
2,035
2
Have you tried solving the equation y" - 4 =0, and then applying the initial conditions?

If y'=0 then there must be no x term in the function f(x)... thus y=C is the only possibility. So then y=1 is the only possibility for the initial conditions given....
Remember, they are not the general expression as a function of x; those are values of the function and its derivative at the point x = 2.
 

cristo

Staff Emeritus
Science Advisor
8,056
72
Ahhh okay I was misreading the damned question, :redface:... I kinda thought it was worded funny... Trying to breeze through my homework too fast I guess.

Sorry! Thanks all, I get it now :-)
 

HallsofIvy

Science Advisor
Homework Helper
41,728
881
It didn't occur to you that is y'= 0 for all x, then y" couldn't be 4!:rolleyes:
 
Yes I knew it was impossible as well. But I figured that the question was not written wrong, I should have reread the question more carefully but I was in too much of a hurry(was due in like 10 minutes). My appologies.
 
Last edited:

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