vectors

A=3i+2j-6k ,

B=2i+4j+7k and

C=2i+9j+3k

the magnitude of vector D=A+B-C is?

$\begin{array}{|rcll|} \hline D &=& A+B-C \\ D &=& (3i+2j-6k)+ (2i+4j+7k)- (2i+9j+3k) \\ D &=& (3+2-2)i+(2+4-9)j+(-6+7-3)k \\ D &=& 3i-3j-2k \\ \left\lVert D \right\rVert &=& \sqrt{3^2+(-3^2)+(-2)^2} \\ \left\lVert D \right\rVert &=& \sqrt{9+9+4} \\ \left\lVert D \right\rVert &=& \sqrt{22} \\ \hline \end{array}$

The magnitude of vector D=A+B-C is $\sqrt{22} = 4.69041575982$