Question 124 of 480
If dy/dx = 2x - 3 and y = 3 when x = 0, find y in terms of x.
- A. 2x2 - 3x
- B. x2 - 3x
- C. x2 - 3x - 3
- D. x2 - 3x + 3
Correct Answer:
D
Explanation
To solve the problem where we have the differential equation \( \frac{dy}{dx} = 2x - 3 \) and the initial condition \( y = 3 \) when \( x = 0 \), we need to find the function \( y \) in terms of \( x \). Let's go through the steps in detail.
### Step 1: Integrate the Differential Equation
The first step is to integrate the right-hand side of the equation to find \( y \). The equation we have is:
\[
\frac{dy}{dx} = 2x - 3
\]
To find \( y \), we integrate both sides with respect to \( x \):
\[
y = \int (2x - 3) \, dx
\]
### Step 2: Perform the Integration
Now, we perform the integration:
1. The integral of \( 2x \) is \( x^2 \).
2. The integral of \( -3 \) is \( -3x \).
Putting it all together, we have:
\[
y = x^2 - 3x + C
\]
where \( C \) is the constant of integration that we need to determine using the initial condition.
### Step 3: Apply the Initial Condition
We know from the problem that when \( x = 0 \), \( y = 3 \). We can use this information to find \( C \):
\[
3 = (0)^2 - 3(0) + C
\]
This simplifies to:
\[
3 = C
\]
### Step 4: Write the Final Equation
Now that we have determined \( C \), we can substitute it back into our equation for \( y \):
\[
y = x^2 - 3x + 3
\]
### Conclusion: Identify the Correct Option
Now, let's compare our final equation \( y = x^2 - 3x + 3 \) with the provided options:
- A. \( 2x^2 - 3x \)
- B. \( x^2 - 3x \)
- C. \( x^2 - 3x - 3 \)
- D. \( x^2 - 3x + 3 \)
The correct option is **D**: \( x^2 - 3x + 3 \).
### Explanation of Incorrect Options
- **Option A: \( 2x^2 - 3x \)**: This option is incorrect because it does not match the integrated function. The coefficient of \( x^2 \) should be 1, not 2.
- **Option B: \( x^2 - 3x \)**: This option is missing the constant term \( +3 \). It does not satisfy the initial condition \( y = 3 \) when \( x = 0 \).
- **Option C: \( x^2 - 3x - 3 \)**: This option has the wrong constant term. It would yield \( y = 0 \) when \( x = 0 \), which does not satisfy the initial condition.
### Revision Summary
- To find \( y \) from \( \frac{dy}{dx} \), integrate the right-hand side.
- Use the initial condition to find the constant of integration.
- The final function is \( y = x^2 - 3x + 3 \).
- Always check each option against the derived function and initial conditions to confirm correctness.