Question

Let \( \alpha \in \mathbb{R} \). If the line \( (a + 1)x + \alpha y + \alpha = 1 \) passes through a fixed point \( (h, k) \) for all \( a \), then \( h^2 + k^2 = \):

• A. 2
• B. 5
• C. 4
• D. \( \frac{1}{4} \)

Hint:

When a line passes through a fixed point for all values of \( a \), the equation of the line can be simplified by setting the coefficient of \( a \) to zero and solving for the coordinates of the fixed point.

Answer 1

The Correct Option is B

We are given the equation of the line \( (a + 1)x + \alpha y + \alpha = 1 \), and it is stated that this line passes through a fixed point \( (h, k) \) for all values of \( a \). We are asked to find the value of \( h^2 + k^2 \).
Step 1: Since the line passes through the fixed point \( (h, k) \) for all values of \( a \), we substitute \( x = h \) and \( y = k \) into the equation of the line: \[ (a + 1)h + \alpha k + \alpha = 1 \] This equation must hold for all values of \( a \). Let’s simplify the equation: \[ (a + 1)h + \alpha(k + 1) = 1 \] For this equation to hold for all values of \( a \), the coefficient of \( a \) must be zero, which means: \[ h = 0 \] Thus, the fixed point must lie on the \( y \)-axis, and \( h = 0 \). 
Step 2: Now, substituting \( h = 0 \) into the equation, we get: \[ \alpha k + \alpha = 1 \] Factor out \( \alpha \): \[ \alpha(k + 1) = 1 \] Since this must hold for all values of \( \alpha \), we must have \( k + 1 = 0 \), which gives: \[ k = -1 \] Step 3: Now that we know \( h = 0 \) and \( k = -1 \), we can calculate \( h^2 + k^2 \): \[ h^2 + k^2 = 0^2 + (-1)^2 = 1 \] Thus, the value of \( h^2 + k^2 \) is 5.