A straight line that intersects two or more straight lines at distinct points is called as transversal.
More clearly,
A straight line intersecting two parallel lines.
From the above figure, we have the following important points.
Vertically opposite angles are equal. |
∠ 1 = ∠ 3 ∠ 2 = ∠ 4 ∠ 5 = ∠ 7 ∠ 6 = ∠ 8 |
Corresponding angles are equal. |
∠ 1 = ∠ 5 ∠ 2 = ∠ 6 ∠ 3 = ∠ 7 ∠ 4 = ∠ 8 |
Alternate interior angles are equal. |
∠ 3 = ∠ 5 ∠ 4 = ∠ 6 |
Alternate exterior angles are equal. |
∠ 1 = ∠ 7 ∠ 2 = ∠ 8 |
Consecutive interior angles are supplementary. |
∠ 3 + ∠ 6 = 180° ∠ 4 + ∠ 5 = 180° |
Same side exterior angles are supplementary. |
∠ 1 + ∠ 8 = 180° ∠ 2 + ∠ 7 = 180° |
Problem 1 :
In the figure given below, let the lines l1 and l2 be parallel and m is transversal. If ∠F = 65°, find the measure of each of the remaining angles.
Solution :
From the given figure,
∠F and ∠H are vertically opposite angles and they are equal.
Then,
∠H = ∠F
∠H = 65°
∠H and ∠D are corresponding angles and they are equal.
Then,
∠D = ∠H
∠D = 65°
∠D and ∠B are vertically opposite angles and they are equal.
Then,
∠B = ∠D
∠B = 65°
∠F and ∠E are together form a straight angle.
Then, we have
∠F + ∠E = 180°
Substitute ∠F = 65°.
65° + ∠E = 180°
∠E = 115°
∠E and ∠G are vertically opposite angles and they are equal.
Then,
∠G = ∠E
∠G = 115°
∠G and ∠C are corresponding angles and they are equal.
Then,
∠C = ∠G
∠C = 115°
∠C and ∠A are vertically opposite angles and they are equal.
Then,
∠A = ∠C
∠A = 115°
Therefore,
∠A = ∠C = ∠E = ∠G = 115°
∠B = ∠D = ∠F = ∠H = 65°
Problem 2 :
In the figure given below, let the lines l1 and l2 be parallel and t is transversal. Find the value of x.
Solution :
From the given figure,
∠(2x + 20)° and ∠(3x - 10)° are corresponding angles.
So, they are equal.
Then,
2x + 20 = 3x - 10
30 = x
Problem 3 :
In the figure given below, let the lines l1 and l2 be parallel and t is transversal. Find the value of x.
Solution :
From the given figure,
∠(3x + 20)° and ∠2x° are consecutive interior angles.
So, they are supplementary.
Then,
3x + 20 + 2x = 180°
5x + 20 = 180°
5x = 160°
x = 32°
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