Angela123 said:A=[1 -4 B=[-3 4
1 -3] -1 c]
For what value of c is it true that AB=I? c =?
I multiplied the two together and got: [1 (4-4c)
0 (4-3c)]
4-4c=1 c=3/4
4-3c=0 c=4/3
Did I do the last step wrong? There is only supposed to be one answer.
A = 1 -4 B = -3 4
1 -3 -1 c
Angela123 said:For what value of c is it true that AB=I? c =?Code:A = [ 1 -4 ] B = [ -3 4 ] [ 1 -3 ] [ -1 c ]
I multiplied the two together and got: [1 (4-4c)
0 (4-3c)]
4-4c=1 c=3/4 <<<<<<<This is wrong
4 - 4c = 0
4c = 4
c = 1
4-3c=0 c=4/3<<<<<<<This is wrong
Angela123 said:So if you are looking for the identity matrix, then you make the equation equal to the number diagonal from it?
Angela123 said:So if you are looking for the identity matrix, then you make the equation equal to the number diagonal from it?
Angela123 said:I was under the impression that the identity matrix is the inverse of A. What I meant by my question was, after I have my equation(s), how do I know what to set them equal to in order to find c? I can see how you got the answer for this one, but suppose it was a 3x3 or 3x2?
Identity matrix is always a square matrix - so [3 x 2] is not possible.
[3 x 3] matrix will be similar - it will have three 1's down the diagonal and 6 zeros every where else.
Angela123 said:I was under the impression that the identity matrix is the inverse of A.
Subhotosh Khan said:Identity matrix has 1 as the diagonal number - and rest are zeros. Incidentally diagonal of a [square] matrix - by definition runs from top left to bottom right.