# 3.E: Number Patterns (Exercises)

- Page ID
- 4900

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#### Exercise \(\PageIndex{1}\): Hexagonal numbers (cornered)

Consider the hexagonal numbers are the sequence \(1,6,15, 28, \cdots.\) Predict the n^{ th} term. Explain your prediction

#### Exercise \(\PageIndex{2}\): Finite sum

For each of the following, find the sum and explain your reasoning. Please do not use any formula.

- \(1+3+5+7+9+\cdots +197+199\)
- \(1+\frac{1}{2}+\frac{1}{4}+\cdots +\frac{1}{2^{16}}+\frac{1}{2^{17}}\)

#### Exercise \(\PageIndex{3}\): Proof by induction

Consider the sequence \( 4,10,16, 22, 28,,\dots\), assume that the pattern continues.

- Show that the \(n^{th}\) term of this sequence can be expressed as \(6n-2\).
- Prove by using induction for all integers \( n \geq 1, 4+10+16+\dots+(6n-2)=n(3n+1)\)

#### Exercise \(\PageIndex{4}\): Proof by induction

Consider the sequence \( 3,11,19, 27, 35,\dots\), assume that the pattern continues.

- Show that the \(n^{th}\) term of this sequence can be expressed as \(8n-5\).
- Prove by using induction for all integers \( n\geq 1, 3+11+19 \dots + (8n-5)=4n^2-n.\)

#### Exercise \(\PageIndex{5}\): Tribonacci

Let's start with the numbers \(0,0,1,\) and generate future numbers in our sequence by adding up the previous three numbers. Write out the first \(15\) terms in this sequence, starting with the first \(1\).

#### Exercise \(\PageIndex{6}\): Proof by induction

The sequence \(b_0,b_1,b_2....\) is defined as follows: \(b_0=1,b_1=3,b_2=5,\) and for any integer \(n \geq 3, \, b_n=3b_{n-2}+2b_{n-3}.\)

- Find \(b_3,b_4,b_5\) and \(b_6\).
- Prove that \(b_n < 2^{n+1}\) for all integers \(n \geq 1.\)

#### Exercise \(\PageIndex{7}\): Quadratic Sequence

Find the \(n^{th}\) term of the sequence \(5,10,17, 26, 37, \cdots\), assume that the pattern continues.

#### Exercise \(\PageIndex{8}\): Proof by induction

Prove by using induction: for all integers \( n\geq 1, \, 1+4+7 \dots + (3n-2)=\frac{n(3n-1)}{2}.\)

#### Exercise \(\PageIndex{9}\): Recognising sequence

Predict \(n^{th}\) term of the sequence \(\frac{2}{3},\frac{3}{4}, \frac{4}{5}\cdots\, assume that the pattern continues. Explain your prediction.

#### Exercise \(\PageIndex{10}\): Recognising sequence

Consider the sequence \( t_1=1, t_2=3+5, t_3=7+9+11, \cdots \). Predict the n^{ th} term. Justify your prediction.

#### Exercise \(\PageIndex{11}\): Proof by induction

Show that the perimeter of the design by joining \(n\) hexagons in a row is \(8n+4\) cm.

#### Exercise \(\PageIndex{13}\): Pentagonal Numbers (cornered)

Find the \(n^{th}\) term of the sequence \(1,5,12, 22, \cdots\),assume that the pattern continues.

#### Exercise \(\PageIndex{14}\): Square Pyramidal numbers

Find the \(n^{th}\) term of the sequence \(1,5,14,30 \cdots\)., assume that the pattern continues.