Question

Can someone explain this particular step?

Answer 1

Where?

Answer 2

wait i am attaching

Answer 3

You have two vectors, \(\left(\dfrac{3}{\sqrt{11}},-\dfrac{1}{\sqrt{11}},\dfrac{1}{\sqrt{11}}\right)\) and \((l,m,n)\), that are said to be perpendicular, which means the dot product of these two vectors is zero:
\[\left(\dfrac{3}{\sqrt{11}},-\dfrac{1}{\sqrt{11}},\dfrac{1}{\sqrt{11}}\right)\cdot(l,m,n)=\frac{3l}{\sqrt{11}}-\frac{m}{\sqrt{11}}+\frac{n}{\sqrt{11}}=0\]and multiplying both sides by \(\sqrt{11}\) gives the first equation,
\[3l-m+n=0\]

Answer 4

Got it!