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Determinants, Inverse Matrice & Solving
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Determinants, Inverse Matrices & Solving. Finding Determinants of Matrices. Notice the different symbol: the straight lines tell you to find the determinant!!. -. (-5 * 2). =. (3 * 4). 12 - (-10). =. 22. =. 2. 0. 1. -2. -1. 4. - PowerPoint PPT Presentation

### Transcript of Determinants, Inverse Matrices & Solving

• Determinants, Inverse Matrices & Solving

• Notice the different symbol:the straight lines tell you to find the determinant!!(3 * 4)-(-5 * 2)12 - (-10) 22=Finding Determinants of Matrices==

• = [(2)(-2)(2) + (0)(5)(-1) + (3)(1)(4)] [(3)(-2)(-1) + (2)(5)(4) + (0)(1)(2)][-8 + 0 +12] --[6 + 40 + 0]4 6 - 40Finding Determinants of Matrices=== -42

• Identity matrix:Square matrix with 1s on the diagonal and zeros everywhere else2 x 2 identity matrix 3 x 3 identity matrix The identity matrix is to matrix multiplication as ___ is to regular multiplication!!!!1

• Multiply: So, the identity matrix multiplied by any matrix lets the any matrix keep its identity!Mathematically, IA = A and AI = A !!

• Inverse Matrix:2 x 2 In words:Take the original matrix. Switch a and d. Change the signs of b and c. Multiply the new matrix by 1 over the determinant of the original matrix.

• =Example: Find the inverse of A.

• Find the inverse matrix.Det A = 8(2) (-5)(-3) = 16 15 = 1 Matrix A

• What happens when you multiply a matrix by its inverse?1st: What happens when you multiply a number by its inverse?A & B are inverses. Multiply them.

• Why do we need to know all this?To Solve Problems!Solve for Matrix X.We need to undo the coefficient matrix.Multiply it by its INVERSE!

• You can take a system of equations and write it with matrices!!!3x + 2y = 112x + y = 8becomes=Coefficient matrixVariable matrixAnswer matrix

• Let A be the coefficient matrix.Multiply both sides of the equation by the inverse of A.=====

• Wow!!!!3x + 2y = 112x + y = 8x = 5; y = -23(5) + 2(-2) = 112(5) + (-2) = 8It works!!!!Check:

• You TrySolve: 4x + 6y = 142x 5y = -9

• You TrySolve: 2x + 3y + z = -13x + 3y + z = 12x + 4y + z = -2

• Real Life Example:You have \$10,000 to invest. You want to invest the money in a stock mutual fund, a bond mutual fund, and a money market fund. The expected annual returns for these funds are given in the table.You want your investment to obtain an overall annual return of 8%. A financial planner recommends that you invest the same amount in stocks as in bonds and the money market combined. How much should you invest in each fund?

• To isolate the variable matrix, RIGHT multiply by the inverse of ASolution: ( 5000, 2500, 2500)

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