In geometry, a direct pair of angles is a pair of surrounding angles created when two lines crossing each other. Surrounding angles are formed when two angles have a common vertex and a typical arm however do no overlap. The direct pair of angles are constantly supplementary together they kind on a directly line. In other words, the amount of two angles in a straight pair is always 180 degrees.

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

When two lines crossing each other at a single point, linear bag of angles are formed. If the angles so developed are surrounding to each various other after the intersection that the two lines, the angle are said to be linear. If two angles type a linear pair, the angles space supplementary, who measures include up to 180°. Hence, a straight pair of angle always add up to 180°.


There space some nature of linear pair of angle that make them unique and different indigenous other varieties of angles. Look at the straight pair of angle properties provided below:

The amount of 2 angles in a linear pair is constantly 180°.

In geometry, there room two species of angle whose sum is 180 degrees. They are linear pairs of angles and supplementary angles. We often say that the direct pair of angles room supplementary, yet do you know that this two varieties of angles space not the same? allow us understand the difference between supplementary angles and linear pair of angles v the table offered below:

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

In the photo below, it have the right to be plainly seen the both the bag of angles room supplementary, yet ∠A and also ∠B space not direct pairs since they room not nearby angles.


The straight pair postulate claims that if a ray stands top top a line, climate the sum of two nearby angles is 180º. Will certainly the converse of this statement it is in true? the is if the sum of a pair of nearby angles is 180º, will certainly the non-common arms of the 2 angles type a line? Yes, the converse is additionally true. These 2 axioms space grouped together as the straight pair axiom. In the figure below, beam QS stand on a line PR forming a direct pair of angles ∠1 and also ∠2.


Important Notes

In a straight pair, if the 2 angles have a common vertex and a common arm, then the non-common side renders a right line and also the sum of the measure up of angle is 180°.Linear pairs are constantly supplementary.

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Example 1: If among the angles creating a direct pair is a best angle, then what deserve to you say about its various other angle?Solution: Let one of the angles creating a linear pair be 'a' and also the various other be 'b'.Given the ∠a = 90° and we already know that straight pairs that angles are supplementary ⇒ ∠a + ∠b = 180°.⇒ 90° + ∠b = 180°⇒ ∠b = 180° - 90°⇒ ∠b = 90°Therefore, in a straight pair that angles, if one of the angle is a best angle then an additional angle is additionally 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 was standing on heat PQ. So, by straight pair axiom, ∠POC + ∠COQ = 180°. However ∠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 room in the ratio of 4:5, then discover the measure of every of the angles.Solution: allow the two angles be 4y and 5y.

We know that linear pair the angles are supplementary ⇒ 4y + 5y = 180°.

9y = 180°

y = 180/9

y = 20

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

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