Math help ? 10 points

a. What is the formula for the determinant of the given matrix expanding by cofactors on the first row?
a b c
d e f
g h i


b. What is the determinant?

Determinant expanding by cofactors on the first row
=a|ei-fh|-b|di-fg|+c|dh-eg|
= aei-afh-bdi+bfg+cdh-ceg