## MIT 1802 – lecture 3 (Multivariable calculus)

This lecture was the first I took notes for from the MIT video series on multivariable calculus.  It covered calculating the inverse of a 3×3 matrix.  The answer is, to invert matrix $A$, find the determinant of $A$ and the adjoint of $A$.

$A^{-1} = \frac{1}{det(A)} adj(A)$

The steps are:

1) find the MINORS (a 3×3 matrix)

2) multiply by the COFACTORS (a +/- matrix alternating with a + in upper left corner)

3) TRANSPOSE the matrix (switch rows and columns)

4) MULTIPLY by one over the determinant of A