What is alternate interior angles?
Let be a set of lines in the plane. A line k is transversal of if # , and # for all . Let be transversal to m and n at points A and B, respectively. We say that each of the angles of intersection of and m and of and n has a transversal side in and a non-transversal side not contained in . Definition: An angle of intersection of m and k and one of n and k are alternate interior angles if their transversal sides are opposite directed and intersecting, and if their non-transversal sides lie on opposite sides of . Two of these angles are corresponding angles if their transversal sides have like directions and their non-transversal sides lie on the same side of . Definition: If k and are lines so that , we shall call these lines non-intersecting. We want to reserve the word parallel for later. Theorem 9.1:[Alternate Interior Angle Theorem] If two lines cut by a transversal have a pair of congruent alternate interior angles, then the two lines are non-intersecting.
Figure 10.1: Alternate interior angles
Proof: Let m and n be two lines cut by the transversal . Let the points of intersection be B and B', respectively. Choose a point A on m on one side of , and choose on the same side of as A. Likewise, choose on the opposite side of from A. Choose on the same side of as C. Hence, it is on the opposite side of from A', by the Plane Separation Axiom. We are given that . Assume that the lines m and n are not non-intersecting; i.e., they have a nonempty intersection. Let us denote this point of intersection by D. D is on one side of , so by changing the labeling, if necessary, we may assume that D lies on the same side of as C and C'. By Congruence Axiom 1 there is a unique point so that . Since, (by Axiom C-2), we may apply the SAS Axiom to prove that
From the definition of congruent triangles, it follows that . Now, the supplement of is congruent to the supplement of , by Proposition 8.5. The supplement of is and . Therefore, is congruent to the supplement of . Since the angles share a side, they are themselves supplementary. Thus, and we have shown that or that is more that one point, contradicting Proposition 6.1. Thus, m and n must be non-intersecting. Corollary 1: If m and n are distinct lines both perpendicular to the line , then m and n are non-intersecting. Proof: is the transversal to m and n. The alternate interior angles are right angles. By Proposition 8.14 all right angles are congruent, so the Alternate Interior Angle Theorem applies. m and n are non-intersecting. Corollary 2: If P is a point not on , then the perpendicular dropped from P to is unique. Proof: Assume that m is a perpendicular to through P, intersecting at Q. If n is another perpendicular to through P intersecting at R, then m and n are two distinct lines perpendicular to . By the above corollary, they are non-intersecting, but each contains P. Thus, the second line cannot be distinct, and the perpendicular is unique. The point at which this perpendicular intersects the line , is called the foot of the perpendicular
If two lines are cut by a transversal to form pairs of congruent corresponding angles congruent alternate interior angles or congruent alternate exterior angles then what are the lines?
An interior angle is an angle defined by two sides of a polygon and that is inside the polygon. Opposite interior angles are specific pairs of interior angles, those that are opposite each other in the polygon. Alternate or opposite interior angles are also angles that lie on opposte sides of the tranversal line that cuts through parallel lines.
When two parallel lines are cut by a transversal angles A and B are alternate interior angles that each measure 105 and deg. What is the measure of each of the other alternate interior angles?
_\_________ .a\b _c\d________ .....\ When a line crosses 2 lines, 8 angles are formed. Four are exterior angles - outside the 2 lines, and four are interior angles. These are labelled a, b, c, d in the diagram. a & d are alternate interior angles because they alternate from one side of the intersecting line to the other; b & c are also alternate interior angles. They are also known as "Z-angles" because the top…
Parallel lines are lines that are coplanar (lying on the same plane) and do not intersect when cut by a transversal, corresponding angles formed by line n are equal in measure, alternate interior angles are equal in measures, the measures of alternate exterior angles are equal, consecutive interior angles are supplementary, consecutive exterior angles are supplementary.
There's lots of useful things you can discover when parallel lines are cut by a transversal, most of them having to do with angle relationships. Corresponding angles are congruent, alternate interior angles are congruent, same side or consecutive interior angles are supplementary, alternate exterior angles are congruent, and vertical angles are congruent.