Inverse & Identity MATRICES Last Updated: October 12, 2005.

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Inverse & Identity MATRICES Last Updated: October 12, 2005

Inverses and Identities 5x = 3

Now with Matrices ? This is the Identity Matrix for 2 x 2 Matrices

Let’s look at another example

What do we multiply a matrix by to get the Identity? New Question ? What do we multiply a matrix by to get the Identity?

The Inverse of a 2x2 Matrix

The Inverse of a 2x2 Matrix

The Inverse of a 2x2 Matrix

A B This is our Formula!

A B This is our Formula!

A B C This is our Formula!

Are the two Matrices Inverses? The product of inverse matrices is the identity matrix. Identity, therefore, INVERSE Matrices

Are the two Matrices Inverses? The product of inverse matrices is the identity matrix. Not the Identity, therefore, NOT INVERSE Matrices

Does the Matrix have an Inverse? Let’s review the definition of the Inverse of a 2x2 Matrix

The Inverse of a 2x2 Matrix

Does the Matrix have an Inverse? Find the determinant! Therefore, NO inverse!

Does the Matrix have an Inverse? Find the determinant! Therefore, an inverse exists!

Does the Matrix have an Inverse? + + 1 2 3 4 5 6 7 8 9 Find the determinant! - - - 1•5•9 + 2•6•7 + 3•4•8 - 7•5•3 - 8•6•1 - 9•4•2 45 + 84 + 96 - 105 - 48 - 72 Therefore, NO inverse!

Does the Matrix have an Inverse? + + 1 3 2 4 Find the determinant! - - - 1•4•2 + 3•1•3 + 2•2•4 - 3•4•2 - 4•1•1 - 2•2•3 8 + 9 + 16 - 24 - 4 - 12 -7 Therefore, an inverse exists!

Solve the system using inverse matrices B 3x + 2y = 7 4x - 5y = 11 This is our Formula!

Solve the system using inverse matrices B 2x - 4y = 9 3x - 2y = 1 This is our Formula!