8.4.3

Finding Missing Angles in Triangles

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Missing Angles in a Triangle

To find a missing angle in a triangle, you need to remember that all the angles add up to 180°.

Equilateral triangle

Equilateral triangle

  • Equilateral triangles have 3 angles.
  • All angles in an equilateral triangle are 60°.
Finding the missing angle

Finding the missing angle

  • You need to remember that the angles in a triangle add up to 180°.
  • You also need to remember that the right angle is 90°.
Finding the missing angle 2

Finding the missing angle 2

  • Add the two known angles together.
    • 40° + 90° = 130°
Finding the missing angle 3

Finding the missing angle 3

  • You know that all the angles in a triangle add up to 180°.
  • You need to work out the difference between 180° and 130°.
    • 180° − 130° = 50°
Finding the missing angle 4

Finding the missing angle 4

  • The missing angle is 50°.

Missing Angles in a Quadrilateral

To find a missing angle in a quadrilateral, you need to remember that all the angles add up to 360°. A quadrilateral is a four-sided shape (e.g. square, rectangle, parallelogram).

Missing angles in quadrilaterals

Missing angles in quadrilaterals

  • Finding missing angles in a quadrilateral is very similar to triangles.
  • But you need to remember that the angles in a quadrilateral add up to 360°.
    • E.g. a square has four right angles (90°).
Finding the missing angle

Finding the missing angle

  • You need to remember that the angles in a quadrilateral add up to 360°.
Finding the missing angle 2

Finding the missing angle 2

  • Add the three known angles together.
    • 96° + 102° + 80° = 278°
Finding the missing angle 3

Finding the missing angle 3

  • You know that all the angles in a quadrilateral add up to 360°.
  • You need to work out the difference between 360° and 278°.
    • 360° − 278° = 82°
Finding the missing angle 4

Finding the missing angle 4

  • The missing angle is 82°.
Jump to other topics
1

Year 5 - Number

1.1

Number & Place Value

1.1.1The Value of Digits to Millions1.1.2Smallest & Biggest Numbers to Millions1.1.3Ordering Numbers to Millions1.1.4Counting in Powers of 101.1.5Counting in Negative Numbers1.1.6Rounding Numbers up to 1,000,0001.1.7Reading Roman Numerals
1.2

Addition & Subtraction

1.2.1Written Methods for Adding Large Numbers1.2.2Written Methods for Subtracting Large Numbers1.2.3Mental Addition & Subtraction1.2.4Rounding to Check Your Answer
1.3

Multiplication & Division

1.3.1Multiples1.3.2Factors1.3.3Prime Numbers1.3.4Prime Factors1.3.5Composite Numbers1.3.6Factor Trees1.3.7Multiplication by a 1 Digit Number1.3.8Long Multiplication Using Column Method1.3.9Times Tables1.3.10Division1.3.11Multiplying & Dividing by 10, 100 & 1,0001.3.12Square & Cube Numbers
1.4

Fractions & Decimals

1.4.1Compare & Order Fractions1.4.2Identifying Equivalent Fractions1.4.3Add & Subtract Fractions1.4.4Mixed Numbers & Improper Fractions1.4.5Multiplying Fractions by Whole Numbers1.4.6Converting Between Decimals & Fractions1.4.7Rounding Decimals1.4.8Ordering Decimals
2

Year 5 - Measurement

2.1

Measures

2.1.1Metric Measurements2.1.2Imperial Measurements
2.2

Perimeter & Area

2.2.1Perimeter2.2.2Area
2.3

Time

2.3.1Units of Time
3

Year 5 - Geometry

3.1

Properties of 3D Shapes

3.1.1Types of 3D Shapes3.1.2Faces, Edges & Vertices
3.2

Properties of 2D Shapes

3.2.1Polygons
3.3

Angles

3.3.1Angles in Degrees3.3.2Types of Angle3.3.3Finding Missing Angles
3.4

Position & Direction

3.4.1Reflection & Translation
4

Year 5 - Statistics

4.1

Graphs

4.1.1Line Graphs4.1.2Tables4.1.3Timetables
5

Year 6 - Number

5.1

Number & Place Value

5.1.1The Value of Digits to Ten Millions5.1.2Ordering Numbers to Millions5.1.3Rounding5.1.4Negative Numbers
5.2

Multiplication & Division

5.2.1Multiplication by a 2 Digit Number5.2.2Division5.2.3Multiples5.2.4Factors5.2.5Primes
5.3

Mental Maths

5.3.1Multiplying & Dividing by 10, 100 & 1,0005.3.2Addition & Subtraction5.3.3Adding & Subtracting 10, 100 & 1,0005.3.4Multiplication & Division
5.4

Order of Operations

5.4.1BIDMAS
5.5

Problem Solving

5.5.1Addition & Subtraction Multi-step Problems5.5.2Problem Solving with Proportion
5.6

Fractions & Decimals

5.6.1Simplifying Fractions Using Equivalents5.6.2Ordering Different Types of Fraction5.6.3Adding & Subtracting Fractions5.6.4Adding & Subtracting Mixed Numbers5.6.5Multiplying Fractions5.6.6Dividing Fractions by Whole Numbers5.6.7Converting Between Decimals & Fractions5.6.8Dividing Decimals
6

Year 6 - Ratio & Proportion

6.1

Ratio

6.1.1Using Ratios6.1.2Simplifying Ratios
6.2

Percentages

6.2.1Calculating Percentages
6.3

Scale

6.3.1Scale of 2D Shapes
7

Year 6 - Algebra

7.1

Sequences

7.1.1Describing Sequences7.1.2Finding Gaps in Sequences
7.2

Missing Number Problems

7.2.1Missing Number Problems
7.3

Equations

7.3.1Balancing Equations7.3.2Combining Two Variables
8

Year 6 - Measurement

8.1

Problem Solving

8.1.1Problem Solving with Measures
8.2

Unit Conversion

8.2.1Conversion Between Miles & Kilometres
8.3

Perimeter, Area & Volume

8.3.1Area8.3.2Volume8.3.3Nets8.3.4Faces, Edges & Vertices
8.4

Angles

8.4.1Types of Angle8.4.2Finding Missing Angles8.4.3Finding Missing Angles in Triangles8.4.4Vertically Opposite Angles
8.5

Circles

8.5.1Parts of a Circle
8.6

Coordinate Grids

8.6.1Positions on Coordinate Grids8.6.2Reflection & Translation
9

Year 6 - Statistics

9.1

Displaying Data

9.1.1Pie Charts9.1.2Line Graphs
9.2

Averages

9.2.1Mean

Practice questions on Finding Missing Angles in Triangles

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What do the angles in a triangle add up to?Multiple choice
  2. 2
    What is the missing angle in this triangle?Multiple choice
  3. 3
    What is the missing angle in this triangle?Multiple choice
  4. 4
    What is the missing angle in this triangle?Multiple choice
  5. 5
    What is the missing angle in this triangle?Multiple choice
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Finding Missing Angles

Vertically Opposite Angles