Matrices

Question 1

Multiply by another matrix

Answer 1

1 2 6 7 1x6 + 2x8 1x7 + 2x9
3 4 x 8 9 = 3x6 + 4x8 3x7 + 4x9

= 22 25
50 57

If the number of columns = the number of rows in the 2nd matrix then you can multiply them

the order of the 2nd matrix is the order of the answer

Question 2

Identity matrix

Answer 2

1 0
0 1

or

1 0 0
0 1 0
0 0 1

Question 3

Determinant

Answer 3

A = 1 2
3 4

|A| = (product of leading diagonal) - product of secondary diagonal)

So, |A| = 1x4 - 2x3 = -2
|A| = -2

Question 4

Matrix Inverse

Answer 4

1. Calculate |A|
2. Swap leading diagonal position
3. change sign on other diagonal. ie + to -. - to +
4. Multiply matrix by 1/|A|