A bisector is a line segment that passes through the vertex of an angle and divides it into two equal angles.

The bisector can appear in a triangle, parallelogram, rhombus and in other geometric figures.

For example, a bisector that passes through an angle of 120° 120° degrees will create two angles of 60° 60° degrees each.

A1  -  Bisector

Suggested Topics to Practice in Advance

  1. Right angle
  2. Acute Angles
  3. Obtuse Angle
  4. Plane angle
  5. Angle Notation

Practice Bisector

Examples with solutions for Bisector

Exercise #1

BD is a bisector.

What is the size of angle ABC?

656565AAABBBCCCDDD

Video Solution

Step-by-Step Solution

Since we are given that the value of angle DBC is 65 degrees, and we know that the angle bisector divides angle ABC into two equal angles, we can calculate the value of angle ABC:

65+65=130 65+65=130

Answer

130

Exercise #2

Calculate angle α \alpha given that it is a bisector.

ααα606060AAAaaa

Video Solution

Step-by-Step Solution

Since an angle bisector divides the angle into two equal angles, and we are given that one angle is equal to 60 degrees. Angle α \alpha is also equal to 60 degrees

Answer

60

Exercise #3

Which of the following figures has a bisector?

Video Solution

Step-by-Step Solution

The answer is C because the angle bisector divides the angle into two equal angles. In diagram C, the angle bisector divides the right angle, which is equal to 90 degrees, into 2 angles that are equal to each other. 45=45 45=45

Answer

4545

Exercise #4

ABCD is a square.

ABC=? ∢\text{ABC}=\text{?}

AAABBBDDDCCC

Video Solution

Step-by-Step Solution

Due to the fact that all angles in a square are equal to 90 degrees, and BC bisects an angle, we can calculate angle ABC accordingly:

90:2=45 90:2=45

Answer

45

Exercise #5

ABCD is a deltoid.

DAC=? ∢DAC=\text{?}

AAABBBCCCDDD2x602x

Video Solution

Step-by-Step Solution

As we know that ABCD is a deltoid, and AC is the bisector of an angle and therefore:

BAC=CAD=2X BAC=CAD=2X

Now we focus on the triangle BAD and calculate the sum of the angles since we know that the sum of the angles in a triangle is 180 degrees:

2X+2X+2X+60=180 2X+2X+2X+60=180

6X+60=180 6X+60=180

18060=6X 180-60=6X

120=6X 120=6X

We divide the two sections by 6:1206=6x6 \frac{120}{6}=\frac{6x}{6}

20=x 20=x

Now we can calculate the angle DAC:

20×2=40 20\times2=40

Answer

30

Exercise #6

ABD=90 ∢\text{ABD}=90

CB bisects ABD \sphericalangle\text{ABD} .

CBD=α \sphericalangle\text{CBD}=\alpha

Calculate the size of ABC ∢ABC .

AAABBBDDDCCCα

Video Solution

Answer

45

Exercise #7

ABD=15 ∢\text{ABD}=15

BD bisects the angle.

Calculate the size of ABC ∢\text{ABC} .

AAABBBCCCDDD15

Video Solution

Answer

30

Exercise #8

Given:

ABC=90 ∢\text{ABC}=90

DBC=45 ∢DBC=45

Is BD a bisector?

AAABBBCCCDDD45

Video Solution

Answer

Yes

Exercise #9

ABC=120 ∢ABC=120

ABD=60 ∢ABD=60

Which of the following are true?

AAABBBCCCDDD60120

Video Solution

Answer

BD bisects ABC ∢ABC .

Exercise #10

Calculate the size of angle α \alpha given that it is a bisector.αααaaa

Video Solution

Answer

45

Exercise #11

BO bisects ABD ∢ABD .

ABD=85 ∢\text{ABD}=85

Calculate the size of

ABO. \sphericalangle ABO\text{.} 85°85°85°AAACCCBBBOOODDD

Video Solution

Answer

42.5

Exercise #12

DBC=90° ∢DBC=90°

BE cross DBA ∢\text{DBA}

Find the value α \alpha

AAABBBCCCDDDEEEα

Video Solution

Answer

45

Exercise #13

The triangle ABC is shown below.

CD bisects C.

Angle C equals 122 degrees.

Calculate angle ACD ∢\text{ACD} .AAABBBCCCDDD

Video Solution

Answer

61°

Exercise #14

Shown below is the triangle ABC.

Angle A is 80 degrees and is intersected by AD.

Calculate angle DAB.

AAABBBCCCDDD

Video Solution

Answer

40°

Exercise #15

The triangle ABC is shown below.

BD bisects B.

Angle B is 66 degrees.

Calculate the angle DBC ∢\text{DBC} AAABBBCCCDDD

Video Solution

Answer

33°

Topics learned in later sections

  1. Sides, Vertices, and Angles
  2. Types of Angles
  3. Sum and Difference of Angles
  4. Sum of Angles in a Polygon
  5. The Sum of the Interior Angles of a Triangle
  6. Exterior angles of a triangle