Finding the Cross Product of A and B: A Puzzling Answer?

In summary, when finding the cross product of two vectors A and B in the x-y plane, the formula is (A_xB_y - A_yB_x)k, where k represents the z-component. In the given problem, A = -3i + 4j and B = 2i + 3j, so the cross product is (-3 x 3 - 4 x 2)k, which simplifies to -17k. The mistake made by the person attempting the problem was forgetting to include a negative sign in the equation.
  • #1
-EquinoX-
564
1

Homework Statement



A = -3i + 4j and B = 2i + 3j

so I want to find AxB

Homework Equations





The Attempt at a Solution



what I got is -9k + 8k, which is -k but the answer solution says it's -17k ?
 
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  • #2
You are missing a negative sign on the 8. Remember that when you take the cross product of two vectors, A and B, in the x-y plane you will get:

[tex](A_xB_y-A_yB_x)\hat{k}[/tex]

You are missing the minus sign in the above equation.
 
  • #3
EDIT: This post refers to a post deleted by the OP.The i x i and j x j terms are zero by definition. You then have:

-9(i x j)+8(j x i)

Remember that the cross product anticommutes. So if ixj=k. What does this mean for j x i?
 
Last edited:
  • #4
jxi is k?
 

Related to Finding the Cross Product of A and B: A Puzzling Answer?

1. What is the cross product of two vectors?

The cross product of two vectors A and B is a vector that is perpendicular to both A and B and has a magnitude equal to the product of their magnitudes multiplied by the sine of the angle between them.

2. How is the cross product calculated?

The cross product of two 3-dimensional vectors A = [a1, a2, a3] and B = [b1, b2, b3] is calculated by taking the determinant of the following matrix:

| i j k |

| a1 a2 a3 |

| b1 b2 b3 |

This results in a vector C = [c1, c2, c3] where c1, c2, and c3 represent the x, y, and z components of the cross product, respectively.

3. What is the significance of the cross product in mathematics and physics?

The cross product is important in both mathematics and physics because it allows us to calculate the direction and magnitude of a vector that is perpendicular to two given vectors. This is useful in many applications, such as calculating torque in physics or finding the normal vector to a plane in mathematics.

4. Can the cross product be applied to vectors in any dimension?

No, the cross product can only be applied to vectors in 3-dimensional space. This is because the determinant method used to calculate the cross product only works for 3x3 matrices.

5. What are some real-life examples of the cross product?

The cross product has many real-life applications, such as determining the direction of torque on a spinning object, calculating the force exerted by a magnetic field on a current-carrying wire, and finding the direction of the normal force on a surface. It is also used in computer graphics to calculate the direction of reflected light on a 3D object.

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