SOLUTION: Let A=[1 3 2 9] , calculate A−1 What in the world do I do with this?! Please help!

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Question 963090: Let A=[1 3
2 9] , calculate A−1
What in the world do I do with this?! Please help!
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
To find the inverse of a 2x2 matrix, first find the determinant.
D=1%289%29-2%283%29=9-6=3
For a 2x2 matrix,
A=%28matrix%282%2C2%2Ca%2Cb%2Cc%2Cd%29%29
the inverse is just,
A%5E%28-1%29=%281%2FD%29%2A%28matrix%282%2C2%2Cd%2C-b%2C-c%2Ca%29%29
So in this case,
A%5E%28-1%29=%281%2F3%29%2A%28matrix%282%2C2%2C9%2C-3%2C-2%2C1%29%29
.
.
A%5E%28-1%29=%28matrix%282%2C2%2C3%2C-1%2C-2%2F3%2C1%2F3%29%29