Matrix Arithmetic, Inverse & Sim Equations, Transformations etc

What are matrices and how do we calculate with them? 

On this page you can find a set of videos, created by Dr James Tanton, that provide an intuitive, conceptual insight into what matrices are, why they are useful and how we calculate with them. Calculating a matrix's inverse and solving simultaneous equations using matrices are also covered [note: the film 'The Matrix' (pause the clip at 34, 58, 66/67, 68/69 and 80 seconds to see 'the matrix'!) was not created by James, nor us! Tok: what's the link between the film and this topic?]

How/why, conceptually, do matrices define transformations. An in-depth look at the geometrical meaning of a matrix's determinant and an introduction to Adjacency matrices follow at the end.
 


Matrices 1: A Natural Appearance/utility

Adjacency Matrices (an introduction) - another Natural use for matrices

Matrices 2: Scalar Multiplication - Naturally!

Matrices 3: Matrix Addition - Naturally!

Matrices 4: Matrix Multiplication .. Naturally!

Matrices 5: Matrix Inverses . . Not as Naturally! (but necessary!)

Matrices 6: Formal Associativity of Matrices

Associative: re-arranging which items you bracket won't change the outcome, as with equations that only contain multiplication or only addition, but not in a calculation with a mix of multiplications and additions.

Mutiplication and addition do not, combined, show associativity e.g. (1+1)x2 ≠ 1+(1x2) [not associative] but (3x4)x5 = 3x(4x5) [associative].

Matrices 7: Solving Simultaneous Equations

Practice question

Simultaneous equation question

Q1) Solve the following (unfriendly) system of equations using matrix methods.

\(\begin{array}{l}3x + 1.7y = e\\3x - 3.3y = \pi \end{array} % MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacaaIZa % GaamiEaiabgUcaRiaaigdacaGGUaGaaG4naiaadMhacqGH9aqpcaWG % LbaabaGaaG4maiaadIhacqGHsislcaaIZaGaaiOlaiaaiodacaWG5b % Gaeyypa0JaeqiWdahaaaa!4647! \)

SOLUTION

Set the matrix: \(A = \left( {\begin{array}{*{20}{c}}3&{1.7}\\3&{ - 3.3}\end{array}} \right) % MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqaiabg2 % da9maabmaabaqbaeqabiGaaaqaaiaaiodaaeaacaaIXaGaaiOlaiaa % iEdaaeaacaaIZaaabaGaeyOeI0IaaG4maiaac6cacaaIZaaaaaGaay % jkaiaawMcaaaaa!401A! \)

Then the system of equations reads:

\(A\left( {\begin{array}{*{20}{c}}x\\y\end{array}} \right) = \left( {\begin{array}{*{20}{c}}e\\\pi \end{array}} \right) % MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqamaabm % aabaqbaeqabiqaaaqaaiaadIhaaeaacaWG5baaaaGaayjkaiaawMca % aiabg2da9maabmaabaqbaeqabiqaaaqaaiaadwgaaeaacqaHapaCaa % aacaGLOaGaayzkaaaaaa!3F8E! \)

The matrix  is invertible and so the system has the unique solution:

\(\left( {\begin{array}{*{20}{c}}x\\y\end{array}} \right) = {A^{ - 1}}\left( {\begin{array}{*{20}{c}}e\\\pi \end{array}} \right) = - \frac{1}{{15}}\left( {\begin{array}{*{20}{c}}{ - 3.3}&{ - 1.7}\\{ - 3}&3\end{array}} \right)\left( {\begin{array}{*{20}{c}}e\\\pi \end{array}} \right) % MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaeWaaeaafa % qabeGabaaabaGaamiEaaqaaiaadMhaaaaacaGLOaGaayzkaaGaeyyp % a0JaamyqamaaCaaaleqabaGaeyOeI0IaaGymaaaakmaabmaabaqbae % qabiqaaaqaaiaadwgaaeaacqaHapaCaaaacaGLOaGaayzkaaGaeyyp % a0JaeyOeI0YaaSaaaeaacaaIXaaabaGaaGymaiaaiwdaaaWaaeWaae % aafaqabeGacaaabaGaeyOeI0IaaG4maiaac6cacaaIZaaabaGaeyOe % I0IaaGymaiaac6cacaaI3aaabaGaeyOeI0IaaG4maaqaaiaaiodaaa % aacaGLOaGaayzkaaWaaeWaaeaafaqabeGabaaabaGaamyzaaqaaiab % ec8aWbaaaiaawIcacaGLPaaaaaa!5416! \)

which gives:

\(\begin{array}{l}x = \frac{1}{{15}}\left( {3.3e + 1.7\pi } \right)\\y = \frac{1}{5}\left( {e - \pi } \right)\end{array} % MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacaWG4b % Gaeyypa0ZaaSaaaeaacaaIXaaabaGaaGymaiaaiwdaaaWaaeWaaeaa % caaIZaGaaiOlaiaaiodacaWGLbGaey4kaSIaaGymaiaac6cacaaI3a % GaeqiWdahacaGLOaGaayzkaaaabaGaamyEaiabg2da9maalaaabaGa % aGymaaqaaiaaiwdaaaWaaeWaaeaacaWGLbGaeyOeI0IaeqiWdahaca % GLOaGaayzkaaaaaaa!4C5A! \)

Bonus Material: Matrix Multiplication is Associative 

Associative: re-arranging which items you bracket won't change the outcome, as with equations that only contain multiplication or only addition, but not in a calculation with a mix of multiplications and additions.

Mutiplication and addition do not, combined, show associativity e.g. (1+1)x2 ≠ 1+(1x2) [not associative] but (3x4)x5 = 3x(4x5) [associative].

IB exam style questions (subscription required for access)

  Matrix Arithemetic, Determinant, Inverse and simultaneous equations :- use these Exam style questions to test if you feel ready, or what you need to review, ahead of moving on to the new topic or your end of unit test/mocks/final exams!

SOLUTIONS to Exam style questions

Matrices 7: Geometric Transformations

Optional Extra: A Full Understanding of one-dimensional Transformations

Click no the "eye" icon  below to view this video.

Some standard Transformations: Reflections, Enlargements/Dilations, Rotations

Identifying Transformations with NO Memorization

Matrices 8: the Geometric Meaning of Determinants

Deeper: Oriented Areas and Negative Determinants


IB exam style questions (subscription required for access)

  Matrix Transformations , use these Exam style questions to test if you feel ready, or what you need to review, ahead of moving on to the new topic or your end of unit test/mocks/final exams!

SOLUTIONS to exam style questions (including a guideline markscheme)

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