9
Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

Embed Size (px)

Citation preview

Page 1: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

Page 2: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

An arithmetic sequence is a sequence with a constant

increase or decrease also known as the constant difference

In the sequence 10, 40, 70, 100, ….

The constant difference between the terms is 30

Page 3: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

A recursive formula for a sequence would be:

a1= first term in the sequencean = term you are trying to findan-1 = previous term in the sequenced = constant difference

Page 4: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

In the sequence 10, 40, 70, 100, ….

The constant difference between the terms is 30

The first term of the sequence is 10

The recursive formula for this sequence would be:

**I plugged in 10 for the first term and 30 for the constant difference**

Write the recursive formula of the sequence 4, 7, 10, 13, ….

Page 5: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

In the sequence 4, 7, 10, 13, ….

To find the 5th term recursively, I plug it into the formula I just made: an = an-1 + 3

a5 = a5-1 + 3 in words: 5th term equals the 4th term plus 3

a5 = 13 + 3

a5 = 16

Page 6: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

A formula that allows you to find the nth term of the sequence by substituting known values in the expression. An explicit formula for sequence would be:

an = a1 + d( n - 1)

a1= first term in the sequencean = current term in the sequence

d = constant differencen = term number

Page 7: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

In the sequence 10, 40, 70, 100, ….

The constant difference between the terms is 30

The first term of the sequence is 10

The explicit formula for this sequence would be:

an = 10 + 30( n - 1) which simplifies to: an = -20 + 30n

**I plugged in 10 for the first term and 30 for the constant difference and distributed**

Write the explicit formula of the sequence 4, 7, 10, 13, ….

an = ___ + ___( n - 1)

Simplify: an = ___ + ___n

Page 8: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

In the sequence 4, 7, 10, 13, ….

To find the 11th term explicitly, I plug in the into the formula I just made:

an = 1 + 3na11 = 1 + 3(11)a11 = 34

Find the 15th term of the sequence using the formula: an = 1 + 3n

Page 9: Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

The first row of the theater has 15 seats in it. Each subsequent row has 3 more seats that the previous row. If the last row has 78 seats, how many rows are in the theater?

Example Test Question

Step 1: Create an explicit formula:

an = 15 + 3( n - 1) which simplifies to: an = 12 + 3n

Step 2: Figure out what you are solving for:the last row number tell you the number of rows in the theater and you know the last row (an) has 78 seats

Step 3: Solve for the last row number:

78 = 12 + 3n 66 = 3n22 = n