Question
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Write an equation for the \( n \)th term of the geometric sequence \( 3,-12,48,-192, \ldots \).

Ask by Stephens Evans. in the United States
Jan 24,2025

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Answer

The \( n \)th term of the sequence is \( a_n = 3 \times (-4)^{n-1} \).

Solution

To find the equation for the \( n \)th term of the geometric sequence \( 3, -12, 48, -192, \ldots \), follow these steps: 1. **Identify the first term (\( a_1 \)) and the common ratio (\( r \)):** - The first term \( a_1 = 3 \). - The common ratio \( r \) is found by dividing the second term by the first term: \[ r = \frac{-12}{3} = -4 \] - To confirm, check the ratio between subsequent terms: \[ \frac{48}{-12} = -4 \quad \text{and} \quad \frac{-192}{48} = -4 \] The common ratio \( r = -4 \) is consistent. 2. **Use the formula for the \( n \)th term of a geometric sequence:** \[ a_n = a_1 \cdot r^{n-1} \] 3. **Substitute the known values into the formula:** \[ a_n = 3 \cdot (-4)^{n-1} \] **Final Equation:** \[ a_n = 3 \cdot (-4)^{\,n-1} \]

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Bonus Knowledge

To find the \( n \)th term of the geometric sequence \( 3, -12, 48, -192, \ldots \), we start by identifying the first term and the common ratio. The first term \( a \) is \( 3 \), and the common ratio \( r \) can be found by dividing the second term by the first term: \[ r = \frac{-12}{3} = -4. \] We can describe the \( n \)th term of a geometric sequence with the formula \( a_n = a \cdot r^{(n-1)} \). Plugging in our values, the equation for the \( n \)th term is: \[ a_n = 3 \cdot (-4)^{(n-1)}. \] So, for this sequence, each term is obtained by multiplying the previous term by \(-4\), resulting in the formula for the \( n \)th term!

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