Can i just find the triple scalar product a.(b x c)
And if it = 0 then it lies in the plane?
Yeah i did something wrong, i used this to help me YouTube - The Cross Product thanks
A short cut for the triple product is this:
If $\displaystyle v_1= <x_1, y_1, z_1>$, $\displaystyle v_2= <x_2, y_2, z_2>$, and [tex]v_3= <x_3, y_3, z_3> then the cross product is the determinant:
$\displaystyle v_1\cdot(v_2\times v_3)= \left|\begin{array}{ccc}x_1 & y_1 & z_1 \\ x_2 & y_2 & z_2 \\ x_3 & y_3 & z_3 \end{array}\right|$