# Math Help - curl

1. ## curl

Find curl(a X f )
a=a(sub1) i + a(sub2) j +a(sub3) k
f=x i + y j +z k

2. If memory serves then

$
\left| \begin{array}{ccc}
i & j & k \\
a_1 & a_2 & a_3 \\
x & y & z \end{array} \right|= i(a_2z-a_3y)-j(a_1z-a_3x)+k(a_1y-a_2x)$

3. Originally Posted by pickslides
If memory serves then

$
\left| \begin{array}{ccc}
i & j & k \\
a_1 & a_2 & a_3 \\
x & y & z \end{array} \right|= i(a_2z-a_3y)-j(a_1z-a_3x)+k(a_1y-a_2x)$
That is $a\times f$. scubasteve123 still needs to take the curl.

But it is far simpler to recognise that, because a is a constant vector,
$\nabla\times (a\times f)= a\times (\nabla\times f)$.