# High School Math : Vector

## Example Questions

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### Example Question #9 : Understanding Vector Calculations

Solve for vector given direction of and magnitude of .     Explanation:

To solve for a vector with the magnitude and direction given, we use the following formula:    ### Example Question #10 : Understanding Vector Calculations

Given vector and , solve for .     Explanation: To solve for , We need to multiply into vector to find ; then we need to subtract the components in the vector and the components together:   ### Example Question #21 : Calculus Ii — Integrals

Find the magnitude of .     Explanation: therefore the vector is To solve for the magnitude:    ### Example Question #22 : Calculus Ii — Integrals

Let  and be the following vectors: and . If is the acute angle between the vectors, then which of the following is equal to ?      Explanation:

The cosine of the acute angle between two vectors is given by the following formula: , where represents the dot product of the two vectors, is the magnitude of vector a, and is the magnitude of vector b.

First, we will need to compute the dot product of the two vectors. Let's say we have two general vectors in space (three dimensions), and . Let the components of be and the components of be . Then the dot product is defined as follows: .

Going back to the original problem, we can use this definition to find the dot product of and .   The next two things we will need to compute are and Let the components of a general vector be . Then is defined as .

Thus, if and , then  and  .

Now, we put all of this information together to find the cosine of the angle between the two vectors. We just need to simplify this.  .

In order to get it completely simplified, we have to rationalize the denominator by multiplying the numerator and denominator by the sqare root of 21.  .

We just have one more step. We need to solve for the value of the angle. In order to do this, we can take the inverse cosine of both sides of the equation.  .

The answer is .

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