00:01
Okay, so to do this, we need to find the inverse matrix of a.
00:05
So i'm going to write a.
00:06
I'm going to write an augmented matrix that on the right side has the identity matrix.
00:13
Now i'm going to get this into row reduced echelon form.
00:16
So i'm going to multiply row two, and i'm going to add it to negative 8, row one, and that's going to become the new row two.
00:28
So i get 1, 2, 1 ,0.
00:34
Negative 8 times 2 is negative 16 plus 18 is 2 and then negative 8 times 1 is negative 8 plus 0 is negative 8 so now here's what we have i'm going to multiply 1 half row 2 and that's going to become the new row 2 so i get 1 0 2 2 1 negative 4 1 1 1 half 0 and then i'm going to take negative row 1 or excuse me negative row 2 negative twice row 2 how about i need to cancel that 2 so i need to take negative twice row 2 and add it to row 1 and that's going to become the new row 1 so i get 0 1 1 here 0 here negative 2 times negative 4 is positive 8 plus 1 is 9 and then negative 2 times 1 half is negative 1 plus 0 is negative 1.
01:52
So here is what we have.
01:55
So my a inverse, my inverse matrix is 9, negative 4, negative 1, 1 1ā2 .5.
02:02
To see that if we did it correctly, let's take 1 ,8, 2, 18, and multiply it by the inverse.
02:11
So we get 1 times 9 is 9 plus 2 times negative 4 is negative 8, 9 plus negative 8 is 1.
02:25
8 times 9 plus negative 8 is 72...