calculate the difference equation whose general solution is Y=(xc)^2-1 with c constant then demonstrate with each of the following functions if they are a solution to said equation and indicate what type of solution it is a) y=x^2 b) y=-1 c)y=x^2+2x
Question
Answer:
To find the difference equation for the given general solution \(Y = (xc)^2 - 1\), we need to find the second-order difference equation that this solution satisfies. A second-order difference equation relates a sequence to its past values. Let's proceed step by step.
The general solution is \(Y = (xc)^2 - 1\).
Now, let's find the first and second differences of \(Y\) with respect to \(x\):
First difference:
\(\Delta Y = Y(x + 1) - Y(x)\)
\(\Delta Y = [(x + 1)c]^2 - 1 - (xc)^2 + 1\)
\(\Delta Y = [c^2(x^2 + 2x + 1) - (xc)^2]\)
\(\Delta Y = c^2x^2 + 2c^2x + c^2 - x^2c^2\)
\(\Delta Y = 2c^2x + c^2\)
Second difference:
\(\Delta^2 Y = \Delta Y(x + 1) - \Delta Y(x)\)
\(\Delta^2 Y = [2c^2(x + 1) + c^2] - [2c^2x + c^2]\)
\(\Delta^2 Y = 2c^2x + 2c^2 + c^2 - 2c^2x - c^2\)
\(\Delta^2 Y = 2c^2\)
So, the second-order difference equation is \(\Delta^2 Y = 2c^2\).
Now, let's test each of the given functions to see if they are solutions to this difference equation:
a) \(y = x^2\):
To check if \(y = x^2\) is a solution, we need to find \(\Delta^2 y\) and see if it equals \(2c^2\).
\(\Delta^2 y = 2\)
Since \(\Delta^2 y\) is not equal to \(2c^2\) for any constant \(c\), \(y = x^2\) is not a solution to the difference equation.
b) \(y = -1\):
To check if \(y = -1\) is a solution, we need to find \(\Delta^2 y\) and see if it equals \(2c^2\).
\(\Delta^2 y = 0\)
Since \(\Delta^2 y\) is not equal to \(2c^2\) for any constant \(c\), \(y = -1\) is not a solution to the difference equation.
c) \(y = x^2 + 2x\):
To check if \(y = x^2 + 2x\) is a solution, we need to find \(\Delta^2 y\) and see if it equals \(2c^2\).
\(\Delta^2 y = 2\)
Since \(\Delta^2 y\) is not equal to \(2c^2\) for any constant \(c\), \(y = x^2 + 2x\) is not a solution to the difference equation.
None of the provided functions is a solution to the given difference equation \(\Delta^2 Y = 2c^2\).
solved
general
11 months ago
1529