Free Grade 3 Working with Identity Matrix Lessons
Free Grade 3 lessons for Working with Identity Matrix: 12 real questions with a full answer key and worked solutions. A matrix is a grid of numbers. For a 2×2 matrix [[a, b], [c, d]], the determinant is ad − bc.
Free
Foundation
35 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- RememberIdentify working with identity matrix
Identify working with identity matrix accurately in a familiar context.
Assessed by: Exit ticket of four short items
- UnderstandExplain working with identity matrix
Explain working with identity matrix accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate working with identity matrix
Calculate working with identity matrix accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare working with identity matrix
Compare working with identity matrix accurately in a familiar context.
Assessed by: Exit ticket of four short items
Prerequisites
Close these gaps first — each has its own free lesson, worksheet and quiz.
How Working with Identity Matrix works
A matrix is a grid of numbers. For a 2×2 matrix [[a, b], [c, d]], the determinant is ad − bc.
12 practice questions
Easy to hard, 24 marks in total. Try them first, then open the answers.
- 1.Find the determinant of [[2, -4], [-1, 2]].[1]
- 2.Find the determinant of [[3, -2], [4, -1]].[1]
- 3.Find the determinant of [[-1, -1], [-4, 3]].[1]
- 4.Find the determinant of [[-4, 1], [-2, -3]].[1]
- 5.Find the determinant of [[5, 1], [2, 2]].[2]
- 6.Find the determinant of [[-1, 6], [5, 4]].[2]
- 7.Find the determinant of [[0, 1], [-1, -2]].[2]
- 8.Find the determinant of [[2, 3], [1, 0]].[2]
- 9.Find the determinant of [[-1, 5], [6, -1]].[3]
- 10.Find the determinant of [[-3, -2], [-4, -2]].[3]
- 11.Find the determinant of [[4, 6], [3, -4]].[3]
- 12.Find the determinant of [[6, 4], [1, 1]].[3]
Show answers and working
1. 0
det = ad − bc. 2 × 2 − -4 × -1 = 0.
2. 5
det = ad − bc. 3 × -1 − -2 × 4 = 5.
3. -7
det = ad − bc. -1 × 3 − -1 × -4 = -7.
4. 14
det = ad − bc. -4 × -3 − 1 × -2 = 14.
5. 8
det = ad − bc. 5 × 2 − 1 × 2 = 8.
6. -34
det = ad − bc. -1 × 4 − 6 × 5 = -34.
7. 1
det = ad − bc. 0 × -2 − 1 × -1 = 1.
8. -3
det = ad − bc. 2 × 0 − 3 × 1 = -3.
9. -29
det = ad − bc. -1 × -1 − 5 × 6 = -29.
10. -2
det = ad − bc. -3 × -2 − -2 × -4 = -2.
11. -34
det = ad − bc. 4 × -4 − 6 × 3 = -34.
12. 2
det = ad − bc. 6 × 1 − 4 × 1 = 2.
Worked examples
Find the determinant of [[3, 2], [4, -2]].
- det = ad − bc.
- 3 × -2 − 2 × 4 = -14.
- Answer: -14
Find the determinant of [[5, -3], [5, 3]].
- det = ad − bc.
- 5 × 3 − -3 × 5 = 30.
- Answer: 30
Find the determinant of [[4, 1], [0, -3]].
- det = ad − bc.
- 4 × -3 − 1 × 0 = -12.
- Answer: -12
Interactive practice
Free, no account required — answer on screen or print it.
Common mistakes
What learners typically get wrong, and how to fix it.
Calculates ab − cd.
Correction: Multiply the diagonals: ad − bc.
Gets signs wrong with negatives.
Correction: Bracket negatives before multiplying.
Teacher tips
- · Colour the two diagonals in different colours.
Parent tips
- · Point out spreadsheets as grids of numbers.
Real-life applications
- · Computer graphics, transformations.
Assessment objectives
How mastery is evidenced, and which standards it maps to.
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Frequently asked
- Is this Grade 3 Working with Identity Matrix lesson really free?
- Yes. Every lessons on FreeMathWorksheet is free to use, print and share — no account, no paywall and no watermark.
- What should a learner already know before this?
- Start with Introducing Identity Matrix, Matrix Multiplication. Each one has its own free lesson, worksheet and quiz.
- How is the lesson sequenced?
- Recognition first, then understanding, application, reasoning and finally mastery — the same ladder used across every free resource on the platform.
- What comes next after Working with Identity Matrix?
- Move on to Identity Matrix in Context, Matrix Addition, Matrix Multiplication, Determinants, which build directly on this idea.
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