# Math Help - Vector multiplication Very urgent: 15 mins

1. ## Vector multiplication Very urgent: 15 mins

Hi. i really need help quick. Im doing a question where I have to find the tangent of a function.

I have 2 vectors r_u and r_v.

$r_u = i + 2uk \ \text{and} \ r_v = j +2vk$

I just need to find the normal vector at the point (1,-1,2) which is given by $r_u * r_v$ but its been so long since ive done this i forgot how to multiply these two.

I have a matrix

i j k
1 0 2u
0 1 2v

after this i have no problem finding the tangent. Please help

2. Hello,

Have a look here : Cross product - Wikipedia, the free encyclopedia

The formula is given :

$\begin{array}{ccc} i & j & k \\ a_1 & a_2 & a_3 \\ b_1 & b_2 & b_3 \end{array}$

The cross product is the determinant of this matrix. Use Sarrus's rule Rule of Sarrus - Wikipedia, the free encyclopedia