Vertically Opposite Angles

What is vertically opposite angles?

When two straight lines intersect each other four angles are formed.

The pair of angles which lie on the opposite sides of the point of intersection are called vertically opposite angles.

In the given figure, two straight lines AB and CD intersect each other at point O. Angles AOD and BOC form one pair of vertically opposite angles; whereas angles AOC and BOD form another pair of vertically opposite angles. 

vertically opposite angles diagram, vertically opposite angles

Vertically opposite angles are always equal.

i.e., ∠AOD = ∠BOC

and ∠AOC = ∠BOD

Note:

opposite angles, vertically opposite angles


In the given figure; rays OM and ON meet at O to form ∠MON (i.e. ∠a) and reflex ∠MON (i.e. ∠b). It must be noted that ∠MON means the smaller angle only unless it is mentioned to take otherwise.


For example; in the given figure, two lines WX and YZ are intersecting at a point O.

vertically opposite angles image, vertically opposite angles



We observe that with the intersection of these lines, four angles have been formed. Angles ∠1 and ∠3 form a pair of vertically opposite angles; while angles ∠2 and ∠4 form another pair of vertically opposite angles.

Clearly, angles ∠1 and ∠2 form a linear pair.

Therefore, ∠1 + ∠2 = 180°

or, ∠1 = 180° - ∠2 …………(i)

again similarly, ∠2 and ∠3 form a linear pair.

Therefore, ∠2 + ∠3 = 180°

or, ∠3 = 180° - ∠2 …………(ii)

From (i) and (ii) we get;

∠1 = ∠3

Similarly, we can prove that ∠2 = ∠4

Thus, if two lines intersect then vertically opposite angles are always equal.

In the below figure, ∠1 and ∠2 are not vertically opposite angles, because their arms do not form two pairs of opposite rays.

vertically opposite angles picture, vertically opposite angles



Now, we will solve various examples on vertically opposite angles.


Worked-out problems on vertically opposite angles:

1. In the given figure, find the measure of unknown angles.

vertically opposite angles problems, vertically opposite angles



Solution:

(i) ∠3= 60° vertically opposite angles

(ii) ∠2 = 90° vertically opposite angles

(iii) ∠2 + ∠1 + 60° = 180° (straight angle)

90° + ∠ 1 + 60° = 180°

150° + ∠ 1 = 180°

Therefore, ∠1 = 180° — 150° = 30°


(iv) ∠1 = ∠4 vertically opposite angles
Therefore, ∠4 = 30°


2. In the given figure, lines PQ, RS, TV intersect at O. If x : y : z = 1 : 2 : 3, then find the values of x, y, z.

problems on vertically opposite angles, vertically opposite angles



Solution:

The sum of all the angles at a point is 360°.

∠POR = ∠SOQ = x° (Pair of vertically opposite angles are equal.)

∠VOQ = ∠POT = y° (Pair of vertically opposite angles are equal.)

∠TOS = ∠ROV = z° (Pair of vertically opposite angles are equal.)

Therefore, ∠POT + ∠POR + ∠ROV + ∠VOQ + ∠QOS + ∠SOT = 360°

y + x + z + y + x + z = 360°

⟹ 2x + 2y + 2z = 360°

⟹ 2(x + y + z) = 360°

⟹ x + y + z = 3̶6̶0̶°/2̶

⟹ x + y + z = 180° --------- (i)

Let the common ratio be a.

Therefore, x = a, y = 2a, z = 3a

Therefore, from the equation (i) we get;

a + 2a + 3a = 180°

⟹ 6a = 180°

⟹ a = 1̶8̶0̶°/6̶

⟹ a = 30°


Therefore, x = a, means x = 30°

y = 2a, means y = 2 × 30 = 60°

z = 3a, means z = 3 × 30 = 90°

Therefore, the measures of the angles are 30°, 60°, 90°.


 Lines and Angles

Fundamental Geometrical Concepts

Angles

Classification of Angles

Related Angles

Some Geometric Terms and Results

Complementary Angles

Supplementary Angles

Complementary and Supplementary Angles

Adjacent Angles

Linear Pair of Angles

Vertically Opposite Angles

Parallel Lines

Transversal Line

Parallel and Transversal Lines







7th Grade Math Problems 

8th Grade Math Practice 

From Vertically Opposite Angles to HOME PAGE




Didn't find what you were looking for? Or want to know more information about Math Only Math. Use this Google Search to find what you need.



New! Comments

Have your say about what you just read! Leave me a comment in the box below. Ask a Question or Answer a Question.




Share this page: What’s this?

Recent Articles

  1. Worksheet on 8 Times Table | Printable Multiplication Table | Video

    Mar 18, 25 03:30 PM

    worksheet on multiplication of 8 times table
    Worksheet on 8 times table can be printed out. Homeschoolers can also use these multiplication table sheets to practice at home.

    Read More

  2. Worksheet on Roman Numerals |Roman Numerals|Symbols for Roman Numerals

    Mar 18, 25 02:47 PM

    Roman Numbers Table
    Practice the worksheet on roman numerals or numbers. This sheet will encourage the students to practice about the symbols for roman numerals and their values. Write the number for the following: (a) V…

    Read More

  3. Conversion of Roman Numeration | Roman Numerals |Hindu Arabic Numerals

    Mar 18, 25 02:12 PM

    We will learn the conversion of Roman numeration. First we will learn how to convert numbers in roman numerals. 1. Convert 579 in roman numerals.

    Read More

  4. Rules of Roman Numeration |Roman Number System|Roman Numeration System

    Mar 18, 25 09:41 AM

    Rules of Roman Numerals
    We will learn about Roman Numeration and its rules. We know that there are seven basic Roman Numerals. They are I, V, X, L, C, D and M. These numerals stand for the number 1, 5, 10, 50, 100, 500

    Read More

  5. Divisible by 2 | Test of Divisibility by 2 |Rules of Divisibility by 2

    Mar 17, 25 04:04 PM

    Divisible by 2
    A number is divisible by 2 if the digit at unit place is either 0 or multiple of 2. So a number is divisible by 2 if digit at its units place is 0, 2, 4, 6 or 8.

    Read More