ΔABC is reflected across line L to form Δ ALBLCL, and A¯¯AL¯¯¯¯ intersects line L at point D. Which equation is not necessarily true?

To determine which equation is not necessarily true, we need to analyze the geometric properties of the given reflection.

Let's break down the information provided:

- ΔABC is reflected across line L to form ΔALBLCL.
- A¯¯AL¯¯¯¯ intersects line L at point D.

When a triangle is reflected across a line, several properties are preserved:
1. Lengths of corresponding sides remain the same.
2. Corresponding angles remain congruent.
3. The midpoint of any side of the original triangle is mapped to the midpoint of the corresponding side of the reflected triangle.

Now, let's consider the equations:

1. AB = DE

This equation relates to the length of corresponding sides. If AB represents a side of ΔABC, and DE represents the corresponding side of ΔALBLCL, then the equation AB = DE must be true by the property of reflections.

2. ∠B = ∠C

This equation relates to the congruency of corresponding angles. If ∠B represents an angle in ΔABC, and ∠C represents the corresponding angle in ΔALBLCL, then the equation ∠B = ∠C must be true by the property of reflections.

3. AC = CL

This equation relates to the length of corresponding sides. While AC and CL are sides in both triangles, there is no guarantee that they are corresponding sides. As a result, the equation AC = CL is not necessarily true in all cases.

4. ∠BAC = ∠BCL

This equation relates to the congruency of corresponding angles. If ∠BAC represents an angle in ΔABC, and ∠BCL represents the corresponding angle in ΔALBLCL, then the equation ∠BAC = ∠BCL must be true by the property of reflections.

Based on our analysis, the equation that is not necessarily true is: AC = CL.