What is the cross product of <-3,0, 8 ><3,0,8> and <-1, -2, 9 ><1,2,9>?

2 Answers
Jun 14, 2017

16hati + 19hatj + 6hatk16ˆi+19ˆj+6ˆk

or

<16,19,6><16,19,6>

Explanation:

For a hand-made explanation on vector multiplication, click here (you can scroll down to the vector/cross product section); it explains basically all you need to know.

If you followed the link, you'll find (somewhere in the cross products section) an explanation about how cross products are found.

In short, you can use the following equation to find its components, using components of the two vectors, which we'll call vecAA and vecBB, and the vector product vecCC:

C_x = A_yB_z - A_zB_yCx=AyBzAzBy

C_y = A_zB_x - A_xB_zCy=AzBxAxBz

C_z = A_xB_y - A_yB_xCz=AxByAyBx

Plugging in the values, we have

C_x = (0)(9) - (8)(-2) = color(red)(16Cx=(0)(9)(8)(2)=16

C_y = (8)(-1) - (-3)(9) = color(blue)(19Cy=(8)(1)(3)(9)=19

C_z = (-3)(-2) - (0)(-1) = color(green)(6Cz=(3)(2)(0)(1)=6

In unit vectors, the cross product is

color(red)(16)hati + color(blue)(19)hatj + color(green)(6)hatk16ˆi+19ˆj+6ˆk

Or alternatively,

color(darkorange)(<16,19,6><16,19,6>

Jun 14, 2017

<16,19,6><16,19,6>

Explanation:

Multiply the major diagonals:

| (color(red)(hati),color(blue)(hatj),color(yellow)(hatk),hati,hatj), (-3,color(red)(0),color(blue)(8),color(yellow)(-3),0), (-1,-2,color(red)(9),color(blue)(-1),color(yellow)(-2)) | =

color(red)((0)(9)hati)+ color(blue)((8)(-1)hatj)+ color(yellow)((-3)(-2)hatk)

Multiply the minor diagonals:

| (hati,hatj,color(yellow)(hatk),color(red)(hati),color(blue)(hatj)), (-3,color(yellow)(0),color(red)(8),color(blue)(-3),0), (color(yellow)(-1),color(red)(-2),color(blue)(9),-1,color(yellow)(-2)) | =

color(red)((0)(9)hati)+ color(blue)((8)(-1)hatj)+ color(yellow)((-3)(-2)hatk)- color(red)((8)(-2)hati) - color(blue)((-3)(9)hatj) - color(yellow)((0)(-1)hatk) =

16hati+19hatj+6hatk

In the original notation <16,19,6>