7. Find r(t) if r'(t) = 6e³ti r(0) = 5i + 3k. + costj + sec²t k and

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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**Problem 7: Find r(t)**

Given: 
\[ \mathbf{r}'(t) = 6e^{3t} \mathbf{i} + \cos(t) \mathbf{j} + \sec^2(t) \mathbf{k} \]

with the initial condition:
\[ \mathbf{r}(0) = 5\mathbf{i} + 3\mathbf{k} \]

To find the position vector \(\mathbf{r}(t)\), we need to integrate \(\mathbf{r}'(t)\).

1. **Integrate the \( \mathbf{i} \) component:**
   \[ \int 6e^{3t} \, dt = 2e^{3t} + C_1 \]

2. **Integrate the \( \mathbf{j} \) component:**
   \[ \int \cos(t) \, dt = \sin(t) + C_2 \]

3. **Integrate the \( \mathbf{k} \) component:**
   \[ \int \sec^2(t) \, dt = \tan(t) + C_3 \]

Thus, the general form of \(\mathbf{r}(t)\) before applying initial conditions is:
\[ \mathbf{r}(t) = (2e^{3t} + C_1) \mathbf{i} + (\sin(t) + C_2) \mathbf{j} + (\tan(t) + C_3) \mathbf{k} \]

Using the initial condition \(\mathbf{r}(0) = 5\mathbf{i} + 3\mathbf{k}\):

- For the \( \mathbf{i} \) component:
  \[ 2e^{0} + C_1 = 5 \]
  \[ 2 + C_1 = 5 \]
  \[ C_1 = 3 \]

- For the \( \mathbf{j} \) component:
  \[ \sin(0) + C_2 = 0 \]
  \[ 0 + C_2 = 0 \]
  \[ C_2 = 0 \]

- For the \( \mathbf{k} \) component:
  \[ \tan(0) + C_3 = 3 \]
  \[ 0 + C_3 = 3 \]
  \[
Transcribed Image Text:**Problem 7: Find r(t)** Given: \[ \mathbf{r}'(t) = 6e^{3t} \mathbf{i} + \cos(t) \mathbf{j} + \sec^2(t) \mathbf{k} \] with the initial condition: \[ \mathbf{r}(0) = 5\mathbf{i} + 3\mathbf{k} \] To find the position vector \(\mathbf{r}(t)\), we need to integrate \(\mathbf{r}'(t)\). 1. **Integrate the \( \mathbf{i} \) component:** \[ \int 6e^{3t} \, dt = 2e^{3t} + C_1 \] 2. **Integrate the \( \mathbf{j} \) component:** \[ \int \cos(t) \, dt = \sin(t) + C_2 \] 3. **Integrate the \( \mathbf{k} \) component:** \[ \int \sec^2(t) \, dt = \tan(t) + C_3 \] Thus, the general form of \(\mathbf{r}(t)\) before applying initial conditions is: \[ \mathbf{r}(t) = (2e^{3t} + C_1) \mathbf{i} + (\sin(t) + C_2) \mathbf{j} + (\tan(t) + C_3) \mathbf{k} \] Using the initial condition \(\mathbf{r}(0) = 5\mathbf{i} + 3\mathbf{k}\): - For the \( \mathbf{i} \) component: \[ 2e^{0} + C_1 = 5 \] \[ 2 + C_1 = 5 \] \[ C_1 = 3 \] - For the \( \mathbf{j} \) component: \[ \sin(0) + C_2 = 0 \] \[ 0 + C_2 = 0 \] \[ C_2 = 0 \] - For the \( \mathbf{k} \) component: \[ \tan(0) + C_3 = 3 \] \[ 0 + C_3 = 3 \] \[
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