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Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

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.

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Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

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  1. Recursive and Explicit Formulas for Arithmetic (Linear) Sequences

  2. 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

  3. A recursive formulafor a sequence would be: a1= first term in the sequence an = term you are trying to find an-1 = previous term in the sequence d = constant difference

  4. 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 formulafor 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, ….

  5. 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

  6. Explicit Formulas A formula that allows you to find the nth term of the sequence by substitutingknown values in the expression. An explicit formulafor sequence would be: • an = a1 + d( n - 1) a1= first term in the sequence an = current term in the sequence d = constant difference n = term number

  7. 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 formulafor 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

  8. 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 + 3n a11 = 1 + 3(11) a11 = 34 Find the 15th term of the sequence using the formula: an = 1 + 3n

  9. Example Test Question 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? 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 = 3n • 22 = n

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