## Thomas' Calculus 13th Edition

$3$
The formula to determine the distance formula for two vectors $a$ and $b$ is given by: $d=\dfrac{| a \cdot b|}{|b|}$ Thus, we have $a \cdot b=-1(-1)+(-2)(-4)+(-2)(0)=9$ and $|a \cdot b|=|9|=9$ Now, $d=\dfrac{9}{ \sqrt {(-1)^2+(-2)^2+(-2)^2}}=\dfrac{9}{3}=3$