2-G

Lines and Angles

• angles
• perpendicular and parallel lines
• exercises
• answers explained

On the Math 1 test, approximately 19 of the 50 questions deal with geometry. Therefore, mastering geometry is crucial for anyone who is taking this test. Of the 19 geometry questions, about 10 of them are on plane geometry; the other 9 are split between solid geometry (3) and coordinate geometry (6), which will be discussed in Sections 2-K and 2-L. Much of the geometry you have learned in your math classes is not covered on the Math 1 test. In this section, we will review all of the important topics in plane geometry that you need to know for the Math 1 test and only those.

Lines are usually referred to by lowercase letters, such as ℓ, m, and n. We can also name a line using two of the points on the line. If A and B are points on line ℓ, we can refer to line ℓ as line $\overleftrightarrow{AB}$.

• $\overrightarrow{AB}$ represents the ray that consists of point A and all the points on $\overleftrightarrow{AB}$ that are on the same side of A as B.
• $\overline{AB}$ represents the line segment that consists of points A and B and all the points on $\overleftrightarrow{AB}$ that are between them.
• Finally, AB represents the length of segment $\overline{AB}$.

TIP

$\overline{AB}\cong \overline{XY}$ means the same thing as AB = XY.

If two line segments have the same length, we say they are congruent. The symbol ≅ is used to indicate congruence, so in the figure below we have $\overline{AB}\cong \overline{XY}$.