diff --git a/41.tex b/41.tex index 14a627a..c433c60 100644 --- a/41.tex +++ b/41.tex @@ -7,10 +7,17 @@ $$A=\pmatrix{1&2\cr3&4}$$ Solution: Apply elementary row operations that turn $A$ into $I$, like this: $$E_3E_2E_1A=I$$ -Multiply both sides of this equation by $A^{-1}$ to prove to yourself that +If you are used to this sort of thing you can see that the product $E_3E_2E_1$ +must be $A^{-1}$ since the whole thing multiplied by $A$ +works out to be the identity matrix $I$. +However, another way to see this is to multiply both sides of the equation +by $A^{-1}$ +and immediately obtain $$E_3E_2E_1=A^{-1}$$ -Use an augmented matrix to apply row operations -to both $A$ and $I$ +Back to the task at hand of finding an inverse, +it is convenient to apply the row operations to an augmented matrix +instead of just $A$. +That way we can do the row operations on both $A$ and $I$ simultaneously. $$\pmatrix{