Question 193 of 480
Find the value of α2 + β2 if α + β = 2 and the distance between points (1, α) and (β, 1)is 3 units
Correct Answer:
D
Explanation
To solve the problem, we need to find the value of \( \alpha^2 + \beta^2 \) given the conditions \( \alpha + \beta = 2 \) and the distance between the points \( (1, \alpha) \) and \( (\beta, 1) \) is 3 units.
### Step 1: Understanding the Distance Formula
The distance \( d \) between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) in a Cartesian plane is given by the formula:
\[
d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}
\]
In our case, the points are \( (1, \alpha) \) and \( (\beta, 1) \). Therefore, we can substitute these points into the distance formula:
\[
d = \sqrt{(\beta - 1)^2 + (1 - \alpha)^2}
\]
### Step 2: Setting Up the Equation
We know that the distance \( d \) is 3 units, so we can set up the equation:
\[
\sqrt{(\beta - 1)^2 + (1 - \alpha)^2} = 3
\]
To eliminate the square root, we square both sides:
\[
(\beta - 1)^2 + (1 - \alpha)^2 = 9
\]
### Step 3: Expanding the Equation
Now, we expand both squares:
\[
(\beta - 1)^2 = \beta^2 - 2\beta + 1
\]
\[
(1 - \alpha)^2 = 1 - 2\alpha + \alpha^2
\]
Substituting these into our equation gives:
\[
\beta^2 - 2\beta + 1 + 1 - 2\alpha + \alpha^2 = 9
\]
Combining like terms results in:
\[
\beta^2 + \alpha^2 - 2\beta - 2\alpha + 2 = 9
\]
Subtracting 2 from both sides:
\[
\beta^2 + \alpha^2 - 2\beta - 2\alpha = 7
\]
### Step 4: Using the Sum of \( \alpha \) and \( \beta \)
We know from the problem statement that \( \alpha + \beta = 2 \). We can express \( \beta \) in terms of \( \alpha \):
\[
\beta = 2 - \alpha
\]
Now, we substitute \( \beta \) into our equation:
\[
(2 - \alpha)^2 + \alpha^2 - 2(2 - \alpha) - 2\alpha = 7
\]
Expanding \( (2 - \alpha)^2 \):
\[
(2 - \alpha)^2 = 4 - 4\alpha + \alpha^2
\]
Substituting this back gives:
\[
4 - 4\alpha + \alpha^2 + \alpha^2 - 4 + 2\alpha - 2\alpha = 7
\]
This simplifies to:
\[
2\alpha^2 - 4\alpha = 7
\]
Rearranging gives:
\[
2\alpha^2 - 4\alpha - 7 = 0
\]
### Step 5: Solving the Quadratic Equation
Now we can use the quadratic formula to solve for \( \alpha \):
\[
\alpha = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
\]
Here, \( a = 2 \), \( b = -4 \), and \( c = -7 \):
\[
\alpha = \frac{4 \pm \sqrt{(-4)^2 - 4 \cdot 2 \cdot (-7)}}{2 \cdot 2}
\]
Calculating the discriminant:
\[
\sqrt{16 + 56} = \sqrt{72} = 6\sqrt{2}
\]
Thus:
\[
\alpha = \frac{4 \pm 6\sqrt{2}}{4} = 1 \pm \frac{3\sqrt{2}}{2}
\]
This gives us two possible values for \( \alpha \):
1. \( \alpha_1 = 1 + \frac{3\sqrt{2}}{2} \)
2. \( \alpha_2 = 1 - \frac{3\sqrt{2}}{2} \)
### Step 6: Finding \( \beta \)
Using \( \beta = 2 - \alpha \):
1. If \( \alpha = 1 + \frac{3\sqrt{2}}{2} \), then \( \beta = 2 - (1 + \frac{3\sqrt{2}}{2}) = 1 - \frac{3\sqrt{2}}{2} \)
2. If \( \alpha = 1 - \frac{3\sqrt{2}}{2} \), then \( \beta = 2 - (1 - \frac{3\sqrt{2}}{2}) = 1 + \frac{3\sqrt{2}}{2} \)
### Step 7: Calculating \( \alpha^2 + \beta^2 \)
Using the identity:
\[
\alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha\beta
\]
We already know \( \