In geometry, a straight pair of angles is a pair of nearby angles developed when two lines crossing each other. Adjacent angles are developed when 2 angles have actually a common vertex and a usual arm but do no overlap. The linear pair of angle are constantly supplementary together they type on a directly line. In various other words, the sum of two angles in a direct pair is constantly 180 degrees.

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1.Definition of direct Pair the Angles
2.Properties of direct Pair of Angles
3.Linear Pair of angles Vs Supplementary Angles
4.Linear Pair Postulate

When two lines crossing each various other at a single point, linear bag of angles room formed. If the angle so formed are surrounding to each various other after the intersection the the 2 lines, the angles are stated to be linear. If two angles form a direct pair, the angles room supplementary, who measures include up to 180°. Hence, a direct pair of angle always add up to 180°.


There space some nature of direct pair of angle that make them unique and also different from other varieties of angles. Look in ~ the direct pair of angles properties noted below:

The amount of 2 angles in a direct pair is always 180°.

In geometry, there space two varieties of angles whose sum is 180 degrees. Lock are linear pairs of angles and supplementary angles. We frequently say that the direct pair of angles are supplementary, but do you know that these two types of angles are not the same? permit us know the difference between supplementary angles and also linear pair the angles with the table provided below:

Linear Pair the AnglesSupplementary Angles
These angles space always surrounding to each other. The means, a pair of angles whose amount is 180 degrees and they lie alongside each various other sharing a usual vertex and a common arm are known as straight pair that angles.These angles need not it is in adjacent. Their sum is additionally 180°.
All direct pairs room supplementary angle too.All supplementary angles space not straight pairs.
Example: ∠1 and also ∠2 in the image provided below.Example: ∠A and ∠B, ∠1 and ∠2 (in the photo below).

In the picture below, it deserve to be plainly seen that both the bag of angles room supplementary, but ∠A and ∠B room not direct pairs due to the fact that they space not nearby angles.


The straight pair postulate claims that if a beam stands top top a line, climate the amount of two nearby angles is 180º. Will certainly the converse that this statement be true? that is if the amount of a pair of adjacent angles is 180º, will the non-common eight of the 2 angles form a line? Yes, the converse is likewise true. These two axioms room grouped with each other as the direct pair axiom. In the number below, ray QS was standing on a heat PR creating a direct pair of angles ∠1 and ∠2.


Important Notes

In a straight pair, if the two angles have actually a usual vertex and a usual arm, climate the non-common side makes a right line and the sum of the measure up of angle is 180°.Linear bag are always supplementary.

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Example 1: If among the angles developing a linear pair is a ideal angle, climate what have the right to you say around its other angle?Solution: Let one of the angles forming a straight pair it is in 'a' and the various other be 'b'.Given that ∠a = 90° and we already know that linear pairs that angles room supplementary ⇒ ∠a + ∠b = 180°.⇒ 90° + ∠b = 180°⇒ ∠b = 180° - 90°⇒ ∠b = 90°Therefore, in a linear pair of angles, if one of the angles is a appropriate angle then an additional angle is likewise a appropriate angle.

Example 2: In the offered figure, if POQ is a right line and also ∠POC = ∠COQ, then present that ∠POC = 90°.


Since beam OC stands on line PQ. So, by straight pair axiom, ∠POC + ∠COQ = 180°. But ∠POC = ∠COQ (given).⇒ ∠POC + ∠POC = 180°⇒ 2∠POC = 180°

⇒ ∠POC = 180°/2 = 90°⇒ ∠POC = 90°Hence Proved.

Example 3: If two angles forming a direct pair space in the proportion of 4:5, then uncover the measure up of every of the angles.Solution: allow the 2 angles it is in 4y and also 5y.

We recognize that linear pair of angles space supplementary ⇒ 4y + 5y = 180°.

9y = 180°

y = 180/9

y = 20

Therefore, the 2 angles are: 4y = 4 × 20 = 80° and 5y = 5 × 20 = 100°.

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