In a parallelogram, one angle is 70°. What are the measures of the other three angles?
- AOption (a)
70°, 70°, 110°
- BOption (b)
110°, 110°, 110°
- COption (c)
70°, 110°, 110°
- DOption (d)
70°, 70°, 70°
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Correct answer
70°, 110°, 110°
Why this answer is correct
Shortcut Trick
In a parallelogram, opposite angles are equal and adjacent angles are supplementary (sum is 180°).
Given angle = 70°
Opposite angle = 70°
Adjacent angle = 180° − 70° = 110°
Angle opposite to the adjacent angle = 110°
The other three angles are 70°, 110°, and 110°.
∴ The correct answer is 70°, 110°, 110°.
Alternate Method
Given:
One angle of the parallelogram = 70°
Formula used:
- Sum of adjacent angles of a parallelogram = 180°
- Opposite angles of a parallelogram are equal.
Let the parallelogram be ABCD where ∠A = 70°.
⇒ ∠A + ∠B = 180° (Adjacent angles are supplementary)
⇒ 70° + ∠B = 180°
⇒ ∠B = 180° − 70°
⇒ ∠B = 110°
Since opposite angles are equal:
⇒ ∠C = ∠A = 70°
⇒ ∠D = ∠B = 110°
∴ The other three angles are 110°, 70°, and 110° (which can be written as 70°, 110°, 110°).
∴ The correct answer is 70°, 110°, 110°.
Additional Information
Sum of Interior Angles
For any quadrilateral, including a parallelogram, the sum of all interior angles is always 360°.
Properties of Diagonals
The diagonals of a parallelogram bisect each other, although they are not necessarily equal in length unless it is a rectangle.
Consecutive Angles
Any pair of consecutive angles in a parallelogram will always sum to 180° because they are interior angles on the same side of a transversal cutting parallel lines.