Exam 5: Induction and Recursion

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Find f(2) and f(3) if f(n)=f(n−1)⋅f(n−2)+1f ( n ) = f ( n - 1 ) \cdot f ( n - 2 ) + 1 f(0)=1, f(1)=4

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f(2)=5, f(3)=21

Use the Principle of Mathematical Induction to prove that 4∣(9n−5n) for all n≥04 \mid \left( 9 ^ { n } - 5 ^ { n } \right) \text { for all } n \geq 0

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P(0):4∣1−1P ( 0 ) : 4 \mid 1 - 1 is true since 4∣0.P(k)→P(k+1):9k+1−5k+1=9(9k−5k)+5k(9−5)4 \mid 0 . \quad P ( k ) \rightarrow P ( k + 1 ) : 9 ^ { k + 1 } - 5 ^ { k + 1 } = 9 \left( 9 ^ { k } - 5 ^ { k } \right) + 5 ^ { k } ( 9 - 5 ) . Each term is divisible by 4:4⌋9k−5k(4 : 4 \rfloor 9 ^ { k } - 5 ^ { k } ( bv P(k))P ( k ) ) and 4 ⌋9−5\rfloor 9 - 5 ,

Give a recursive algorithm for computing na, where n is a positive integer and a is a real number. n a \text {, where } n \text { is a positive integer and } a \text { is a real number. }

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The following procedure computes na: procedure mult( aa : real number, nn : positive integer)
if n=1n = 1 then mult (a,n):=a( a , n ) : = a
else mult⁡(a,n):=a+mult⁡(a,n−1)\operatorname { mult } ( a , n ) : = a + \operatorname { mult } ( a , n - 1 ) .

Use the Principle of Mathematical Induction to prove that 1+3+9+27+⋯+3n=3n+1−12 for all n≥01 + 3 + 9 + 27 + \cdots + 3 ^ { n } = \frac { 3 ^ { n + 1 } - 1 } { 2 } \text { for all } n \geq 0

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Describe a recursive algorithm for computing 33n where n is a nonnegative integer. 3 ^ { 3 ^ { n } } \text { where } n \text { is a nonnegative integer. }

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Use the Principle of Mathematical Induction to prove that 1+4+7+10+⋯+(3n−2)=n(3n−1)2 for all 1 + 4 + 7 + 10 + \cdots + ( 3 n - 2 ) = \frac { n ( 3 n - 1 ) } { 2 } \text { for all } n ≥ 1.

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Suppose {an} is defined recursively by an=an−12−1 and that a0=2. Find a3 and a4. \left\{ a _ { n } \right\} \text { is defined recursively by } a _ { n } = a _ { n - 1 } ^ { 2 } - 1 \text { and that } a _ { 0 } = 2 \text {. Find } a _ { 3 } \text { and } a _ { 4 } \text {. }

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Find the error in the following proof of this "theorem": "Theorem: Every positive integer equals the next largest positive integer." "Proof: Let P(n) be the proposition ′n=n+1′' n = n + 1 ' To show that P(k)→P(k+1)P ( k ) \rightarrow P ( k + 1 ) assume that P(k) is true for some k , so that k=k+1 . Add 1 to both sides of this equation to obtain k+1=k+2 , which is P(k+1) . Therefore P(k)→P(k+1)P ( k ) \rightarrow P ( k + 1 ) is true. Hence P(n) is true for all positive integers n . "

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Find f(2) and f(3) if f(n)=2f(n−1)+6,f(0)=3f ( n ) = 2 f ( n - 1 ) + 6 , f ( 0 ) = 3

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Use the Principle of Mathematical Induction to prove that 5∣(7n−2n) for all n≥05 \mid \left( 7 ^ { n } - 2 ^ { n } \right) \text { for all } n \geq 0

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Floor borders one foot wide and of varying lengths are to be covered with nonoverlapping tiles that are available in two sizes: 1′×3′ and 1′×5′1 ^ { \prime } \times 3 ^ { \prime } \text { and } 1 ^ { \prime } \times 5 ^ { \prime } sizes. Assuming that the supply of each size is infinite, prove that every 1′×n′1 ^ { \prime } \times n ^ { \prime } border (n > 7) can be covered with these tiles.

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Use the Principle of Mathematical Induction to prove that 2n+3≤2n for all n≥4. 2 n + 3 \leq 2 ^ { n } \text { for all } n \geq 4 \text {. }

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In questions give a recursive definition with initial condition(s) of the set S. -  The set of strings 1,111,11111,1111111,…\text { The set of strings } 1,111,11111,1111111 , \ldots

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give a recursive definition (with initial condition(s)) of {an}(n=1,2,3,…)\left\{ a _ { n } \right\} ( n = 1,2,3 , \ldots ) - an=2na _ { n } = 2 ^ { n }

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Use the Principle of Mathematical Induction to prove that 1+2n≤3n for all n≥11 + 2 ^ { n } \leq 3 ^ { n } \text { for all } n \geq 1

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Use the Principle of Mathematical Induction to prove that n3>n2+3 for all n≥2n ^ { 3 } > n ^ { 2 } + 3 \text { for all } n \geq 2

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Use the Principle of Mathematical Induction to prove that 1−2+22−23+⋯+(−1)n2n=2n+1(−1)n+131 - 2 + 2 ^ { 2 } - 2 ^ { 3 } + \cdots + ( - 1 ) ^ { n } 2 ^ { n } = \frac { 2 ^ { n + 1 } ( - 1 ) ^ { n } + 1 } { 3 } for all positive integers n .

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Use the Principle of Mathematical Induction to prove that 2∣(n2+3n) for all n≥12 \mid \left( n ^ { 2 } + 3 n \right) \text { for all } n \geq 1

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Suppose that the only paper money consists of 3-dollar bills and 10-dollar bills. Show that any dollar amount greater than 17 dollars could be made from a combination of these bills.

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In questions give a recursive definition with initial condition(s) of the set S. - {0.1,0.01,0.001,0.0001}\{ 0.1,0.01,0.001,0.0001 \}

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