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\( \sum _ { p = 0 } ^ { m } 3 ( 2 ) ^ { 2 p - 3 } < 8000 \)

Ask by Weber Thornton. in South Africa
Jan 23,2025

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Tutor-Verified Answer

Answer

\( m = 6 \)

Solution

To solve the inequality: \[ \sum_{p=0}^{m} 3 \cdot 2^{2p - 3} < 8000 \] **Step 1: Simplify the Sum** First, simplify the expression inside the summation: \[ 3 \cdot 2^{2p - 3} = 3 \cdot \frac{2^{2p}}{2^3} = \frac{3}{8} \cdot 4^p \] So, the sum becomes: \[ \sum_{p=0}^{m} \frac{3}{8} \cdot 4^p = \frac{3}{8} \sum_{p=0}^{m} 4^p \] **Step 2: Use the Geometric Series Formula** The sum of a geometric series \(\sum_{p=0}^{m} ar^p\) is given by: \[ \sum_{p=0}^{m} ar^p = a \cdot \frac{r^{m+1} - 1}{r - 1} \] In this case, \(a = \frac{3}{8}\) and \(r = 4\): \[ \frac{3}{8} \cdot \frac{4^{m+1} - 1}{4 - 1} = \frac{4^{m+1} - 1}{8} \] **Step 3: Set Up the Inequality** Set the simplified sum less than 8000: \[ \frac{4^{m+1} - 1}{8} < 8000 \] Multiply both sides by 8: \[ 4^{m+1} - 1 < 64000 \] Add 1 to both sides: \[ 4^{m+1} < 64001 \] **Step 4: Solve for \(m\)** Find the largest integer \(m\) such that \(4^{m+1} < 64001\). Calculate powers of 4: \[ 4^7 = 16384 \quad \text{and} \quad 4^8 = 65536 \] Since \(4^8 = 65536 > 64001\), the largest integer \(m+1\) can be is 7. Therefore: \[ m + 1 \leq 7 \implies m \leq 6 \] **Verification:** - For \(m = 6\): \[ \frac{4^{7} - 1}{8} = \frac{16384 - 1}{8} = \frac{16383}{8} = 2047.875 < 8000 \] - For \(m = 7\): \[ \frac{4^{8} - 1}{8} = \frac{65536 - 1}{8} = \frac{65535}{8} = 8191.875 > 8000 \] Thus, the largest integer \(m\) satisfying the inequality is **6**. **Answer:** \( m = 6 \)

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The Deep Dive

To solve the inequality \( \sum _ { p = 0 } ^ { m } 3 ( 2 ) ^ { 2 p - 3 } < 8000 \), we first recognize the series as a geometric series. The general term can be simplified to \( 3 \cdot 2^{2p-3} = \frac{3}{8} \cdot (2^2)^p = \frac{3}{8} \cdot 4^p \). The sum of the series can be computed as follows: \[ \sum_{p=0}^{m} 3(2)^{2p - 3} = \frac{3}{8} \sum_{p=0}^{m} 4^p \] The sum of a geometric series \( \sum_{p=0}^{m} r^p \) is given by \( S = \frac{r^{m + 1} - 1}{r - 1} \). Here, \( r = 4 \): \[ \sum_{p=0}^{m} 4^p = \frac{4^{m + 1} - 1}{4 - 1} = \frac{4^{m + 1} - 1}{3} \] Substituting back, we have: \[ \sum_{p=0}^{m} 3(2)^{2p - 3} = \frac{3}{8} \cdot \frac{4^{m + 1} - 1}{3} = \frac{4^{m + 1} - 1}{8} \] Now, we can set up our inequality: \[ \frac{4^{m + 1} - 1}{8} < 8000 \] Multiplying both sides by 8 gives: \[ 4^{m + 1} - 1 < 64000 \] Adding 1: \[ 4^{m + 1} < 64001 \] To solve for \( m \), we take logarithms: \[ m + 1 < \log_4(64001) \] Since \( \log_4(64001) = \frac{\log_{10}(64001)}{\log_{10}(4)}\). Calculating \( \log_{10}(64001) \approx 4.806 \) and \( \log_{10}(4) \approx 0.602 \): \[ \log_4(64001) \approx \frac{4.806}{0.602} \approx 7.98 \] Thus, \[ m + 1 < 7.98 \quad \Rightarrow \quad m < 6.98 \] This means the largest integer \( m \) is 6. To summarize, the maximum value of \( m \) that satisfies the original inequality is 6.

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