Which of the following correctly uses the explicit formula, An=1/4+(n−1)⋅1/2

, to find the 9th term of the described arithmetic sequence?(1 point)
Responses

814
8 Start Fraction 1 over 4 End Fraction

434
4 Start Fraction 3 over 4 End Fraction

414
4 Start Fraction 1 over 4 End Fraction

834

1 answer

To find the 9th term of the arithmetic sequence using the explicit formula \( A_n = \frac{1}{4} + (n - 1) \cdot \frac{1}{2} \), we need to substitute \( n = 9 \) into the formula.

Let's calculate \( A_9 \):

\[ A_9 = \frac{1}{4} + (9 - 1) \cdot \frac{1}{2} \] \[ = \frac{1}{4} + 8 \cdot \frac{1}{2} \] \[ = \frac{1}{4} + 4 \] \[ = \frac{1}{4} + \frac{16}{4} \quad \text{(converting 4 to have a common denominator)} \] \[ = \frac{1 + 16}{4} \] \[ = \frac{17}{4} \]

Now let's examine the responses:

  1. 814
  2. 8 Start Fraction 1 over 4 End Fraction (which represents \( 8 \frac{1}{4} = \frac{33}{4} \))
  3. 434
  4. 4 Start Fraction 3 over 4 End Fraction (which represents \( 4 \frac{3}{4} = \frac{15}{4} \))
  5. 414
  6. 4 Start Fraction 1 over 4 End Fraction (which represents \( 4 \frac{1}{4} = \frac{17}{4} \))
  7. 834

The correct answer is 4 Start Fraction 1 over 4 End Fraction, which simplifies to \( \frac{17}{4} \).