Suppose that the sequence x0, x1, x2... is defined by x0 = 3, x1 = 7, and xk+2 = xk+1+20xk for k?0. Find a general formula for xk.
I don't even know how to start this.
Thanks!
Solution:
Since is a linear homogeneous recurrence , the characteristic equation is
Divide both side by we get
So , by the Theorem : r is the solution of if and only if is the solution of we have ,
and are the solution to the given recurrence.
by principle of superposition any linear combination of the solutions is also a solution we have
is also a solution.
Now , using the initial conditions and we get
On solving simultaneously we get
The general formula is
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