HP 39gs Master Manual page 213

Finding an inverse matrix
Eg. 2 Find the inverse matrix
The first step is to store the matrix A into
inverse into you will find, depending on the determinant, that the
M2
result is probably a collection of decimal values (see right).
This answer is correct and we could stop there. However, this is not the
best way to display the answer. The fact that the determinant is
incorporated into the inverse makes whole numbers unlikely.
A better way is often to write the answer as a fraction
by a matrix of whole numbers. If we multiply the inverse by the determinant then we can usually remove the
fractions.
i.e.
Thus we can finally write:
An alternative to this is to change into Fraction 6 numeric format in the
view. This will give a matrix of fractional values which can be
MODES
seen more clearly using
for the matrix A = ⎢ ⎢ 1
−
1
A
. If you now simply store its
M1
with being...
M2
⎡ −13
17
⎢ −5
1
A =
6
7 ⎢
−
⎢ 6
−10
⎣
.
213
⎡ 2 4 ⎤
1
3 ⎥ ⎥
1
⎢ −2 4 −1 ⎥ ⎦
⎣
1
multiplied
( )
det A
−1 ⎤
−2 ⎥ ⎥
1 ⎥ ⎦