$\text{a) C=( -1 ) . ( -2 ) . ( -3 ) . ( -4 ) . ( -5 ) . b}$
$\text{Thay b = 8 vào ta được:}$
$\text{C = ( -1 ) . ( -2 ) . ( -3 ). ( -4 ) . ( -5 ) . 8}$
$\text{C = - ( 1 . 2 . 3 . 4 . 5 . 8 )}$
$\text{C = - ( 120 . 8 )}$
$\text{C = -960}$
$\text{b) C = ( -8 ) . 25 . ( -2 ) . 4 . ( -5 ) . b}$
$\text{Thay b = -125 vào ta được:}$
$\text{C= ( - 8 ) . 25 . ( -2 ) . 4 . ( -5 ) . (-125 )}$
$\text{C= 8 . 25 . 2 . 4 . 5 . 125}$
$\text{C = ( 8 . 125 ) . ( 25 . 4 ) . ( 2 . 5 )}$
$\text{C= 1000 . 100 . 10}$
$\text{C = 1000000}$.
