Have we ever seen this phenomenon before? Let’s do some quick multiplication…
What do we call this? 5 __= 5 the (multiplicative) identity 1 Let’s do some quick multiplication…
What will we call this? Identity Matrix I Let’s do some quick multiplication…
Identity Matrix 2x2 Identity Matrix 3x3 Identity Matrix
Identity Matrix AI= A IA= A Any matrix multiplied by the identity matrix will be equal to itself.
Identity Matrix Or
Inverse Matrix A * A -1 = I Any matrix multiplied by its inverse will be the identity matrix.
Solving Systems using Matrices
Matrix Equation A linear system can be written as a matrix equation AX=B Coefficient matrix Variable matrix Answer matrix
Ex. 1 Write as a matrix equation.
Suppose ax = b How do you solve for x? We cannot divide matrices, but we can multiply by the inverse. AX = B A -1 A -1 IX = A -1 B A -1 X = A -1 B Solving Matrix Equations
Ex. 2 Solve using matrices. x = -7 y = -4 A B A -1 X = A -1 B AX = B (-7, -4)
Ex. 3 Solve using matrices x = 5/7 y = 2 (5/7, 2)
Ex. 4 Solve using matrices x = 2 y = -1 z = -2 (2, -1, -2)
Ex. 5 Solve using matrices x = 4 y = -7 z = 2 (4, -7, 2)