Summary

When two lines intersect, they form angles. The vertically opposite angles are and the linear pairs add up to °.

When two lines intersect and the angles formed are (i.e., all four angles are equal), the lines are said to be to each other.

When two lines never intersect on a plane, they are called lines.

When a line t intersects another pair of lines, it is called a and it forms sets of 4 angles. Each of the 4 angles in the first set has a angle in the second set.

When a transversal intersects a pair of parallel lines, the corresponding angles are . When a transversal intersects a pair of lines and the corresponding angles are equal, then the pair of lines is .

When a transversal intersects a pair of parallel lines, the alternate angles are .

The interior angles on the same side formed by a transversal intersecting a pair of parallel lines always add up to .