Chapter 10: Problem 6
Paul invested the stock profits he received 15 years ago in an account that paid \(8 \%\) interest compounded quarterly. If his account now has \(\$ 7218.27\) in it, what was his initial investment?
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Chapter 10: Problem 6
Paul invested the stock profits he received 15 years ago in an account that paid \(8 \%\) interest compounded quarterly. If his account now has \(\$ 7218.27\) in it, what was his initial investment?
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$$ \text { Prove that any two consecutive Fibonacci numbers are relatively prime. } $$
Solve the following recurrence relations. a) \(a_{n+2}+3 a_{n+1}+2 a_{n}=3^{n}, \quad n \geq 0, a_{0}=0, a_{1}=1\) b) \(a_{n+2}+4 a_{n+1}+4 a_{n}=7, \quad n \geq 0, \quad a_{0}=1, a_{1}=2\) c) \(a_{n+2}-a_{n}=\sin (n \pi / 2), \quad n \geq 0, a_{0}=1, a_{1}=1\)
For \(n \in \mathbf{Z}^{+}, d_{n}\) denotes the number of derangements of \(\\{1,2,3, \ldots, n\\}\), as discussed in Section \(8.3\). a) If \(n>2\), show that \(d_{n}\) satisfies the recurrence relation $$ d_{n}=(n-1)\left(d_{n-1}+d_{n-2}\right), \quad d_{2}=1, \quad d_{1}=0 . $$ b) How can we define \(d_{0}\) so that the result in part (a) is valid for \(n \geq 2 ?\) c) Rewrite the result in part (a) as \(d_{n}-n d_{n-1}=\) \(-\left[d_{n-1}-(n-1) d_{n-2}\right]\). How can \(d_{n}-n d_{n-1}\) be expressed in terms of \(d_{n-2}, d_{n-3}\) ? d) Show that \(d_{n}-n d_{n-1}=(-1)^{n}\). e) Let \(f(x)=\sum_{n=1}^{\infty}\left(d_{n} x^{n}\right) / n !\). After multiplying both sides of the equation in part (d) by \(x^{n} / n\) ! and summing for \(n \geq 2\), verify that \(f(x)=\left(e^{-x}\right) /\) \((1-x)\). Hence $$ d_{n}=n !\left[1-\frac{1}{1 !}+\frac{1}{2 !}-\frac{1}{3 !}+\cdots+\frac{(-1)^{n}}{n !}\right] $$
Find and solve a recurrence relation for the number of ways to park motorcycles and compact cars in a row of \(n\) spaces if each cycle requires one space and each compact needs two. (All cycles are identical in appearance, as are the cars, and we want to use up all the \(n\) spaces.)
Solve the following recurrence relations by the method of generating functions. a) \(a_{n+1}-a_{n}=3^{n}, \quad n \geq 0, a_{0}=1\) b) \(a_{n+1}-a_{n}=n^{2}, \quad n \geq 0, a_{0}=1\) c) \(a_{n}-3 a_{n-1}=5^{n-1}, \quad n \geq 1, \quad a_{0}=1\) d) \(a_{n+2}-3 a_{n+1}+2 a_{n}=0, \quad n \geq 0, \quad a_{0}=1, \quad a_{1}=6\) e) \(a_{n+2}-2 a_{n+1}+a_{n}=2^{n}, \quad n \geq 0, a_{0}=1, a_{1}=2\)
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