In the given figure, AB is parallel to CD and RS is a transversal. Find the value of X.

- AOption (a)
55
- BOption (b)
65
- COption (c)
35
- DOption (d)
45
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Correct answer
55
Why this answer is correct
Shortcut Trick
When two parallel lines are intersected by a transversal, the corresponding angles are always equal.
In the figure, X and the given angle 55° are corresponding angles.
∴ X = 55.
∴ The correct answer is 55.
Alternate Method
Given: AB ∥ CD and RS is a transversal.
Formula Used: Property of Corresponding Angles in parallel lines.
Calculations:
⇒ Let the point of intersection of RS with AB be P and with CD be Q.
⇒ Since AB ∥ CD, the angles at the same relative position at each intersection are corresponding angles.
⇒ ∠BPS and ∠DQS are corresponding angles.
⇒ Property: ∠BPS = ∠DQS
⇒ X = 55°
∴ The correct answer is 55.
Additional Information
Alternate Interior Angles
When a transversal cuts parallel lines, the pairs of angles on opposite sides of the transversal and between the parallel lines are equal.
Consecutive Interior Angles
Also known as co-interior angles, these are on the same side of the transversal and their sum is always 180° for parallel lines.
Vertically Opposite Angles
Angles opposite each other at a vertex where two lines intersect are always equal, regardless of parallel lines.