3. "When two lines intersect at a 90 degree angle, they are called perpendicular." Which of the words in the previous sentence is an undefined term used in geometry? a. Intersect b. Degree c. Lines d. Perpendicular

## Step 1<br />In geometry, there are certain terms that are not defined but are understood intuitively. These terms are known as undefined terms. They include concepts such as points, lines, and planes.<br /><br />## Step 2<br />In the given sentence, "When two lines intersect at a 90 degree angle, they are called perpendicular," the term "lines" is an undefined term. This is because it is a fundamental concept in geometry that is not defined but is understood intuitively.<br /><br />## Step 3<br />The other options, "intersect", "degree", and "perpendicular", are not undefined terms. "Intersect" is a defined term, "degree" is a defined term, and "perpendicular" is a defined term.