Question

definition of median
definition of perpendicular lines
lines that arent parallel intersect
definition of midpoint
midsegment theorem
definition of a parallelogram
properties of a parallelogram
not quite. try again.

Explanation:

To solve this, we analyze each option:

• "Definition of median": Median in geometry (not statistics here) relates to a line from a vertex to the midpoint of the opposite side, relevant for triangle midsegments/parallelograms? Maybe, but let's check others.
• "Definition of perpendicular lines": Perpendicular lines form 90° angles. This is not relevant to midsegments, midpoints, or parallelogram properties (unless the figure is a rectangle, but the core concepts here are midpoints, midsegments, parallelograms). So this is incorrect.
• "Lines that aren’t parallel intersect": In Euclidean geometry, non - parallel coplanar lines intersect, but this is a general line - intersection rule, not specific to the key concepts (midpoint, midsegment, parallelogram) here. So incorrect.
• "Definition of midpoint": A midpoint divides a segment into two equal parts, essential for midsegments and parallelogram properties (e.g., diagonals bisect each other). Correct to include.
• "Midsegment Theorem": The midsegment of a triangle is parallel to the third side and half its length, relevant for connecting to parallelogram properties (since a midsegment creates a parallelogram). Correct to include.
• "Definition of a parallelogram": A quadrilateral with both pairs of opposite sides parallel, fundamental to the topic. Correct to include.
• "Properties of a parallelogram": Such as opposite sides equal, diagonals bisect each other, relevant. Correct to include.

The incorrect checked option is "Definition of median" (median in geometry is a line from a vertex to the midpoint of the opposite side, but if the problem is about midsegments/parallelograms, the "median" here (if misapplied from statistics or mis - context) is incorrect. Also, the unchecked options: "Definition of perpendicular lines" and "Lines that aren’t parallel intersect" are not relevant. But the main error is "Definition of median" being checked (if the topic is about midsegments, midpoints, parallelograms, the geometric median is a line, but maybe the problem is about triangle midsegments/parallelograms where "median" was mis - selected).

To correct, uncheck "Definition of median" (as it’s not relevant to the core concepts of midpoint, midsegment, and parallelogram properties here) and check if any others were missed, but the key wrong check is "Definition of median".

Answer:

Uncheck "Definition of median" (the first checked option) and leave the other correct checks ("Definition of midpoint", "Midsegment Theorem", "Definition of a parallelogram", "Properties of a parallelogram") as is. The incorrect checked option is "Definition of median".