Grasple has multiple check methods using the Computer Algebra System (CAS) which can be used within the editor to indicate when the answer of a student should be marked correct/incorrect. A full list of current options can be found in this article.

1. When to use the Parallel to check?
2. Example cases
3. An example exercise
4. How does the Parallel to check work?

## When to use the parallel to check?

If you want to check whether the student answer is a vector and that vector is parallel to a given vector, you should use this check. A simple example would be: "vector(1, 2, 1)" is parallel to "vector(2, 4, 2)" but not to "vector(1, -2, 1)".

If you only want to check whether the vector is algebraically equal (e.g. "vector(1, 2, 1)" is equal to "vector(1, 1+1, 1)"), use the Algebraically Equivalent check.

## Example cases

The method uses similar logic as the Algebraically Equivalent check for vectors. In addition it also checks whether the vectors are parallel, allowing more answers to be marked as correct. ## An example exercise

The following steps describe in short how to do this.

1. Create a new exercise with type "Math".
2. Set the check type of the exercise by changing the answer rule relation to "Parallel to". Read more about answer rules here.
3. Give a vector (either column or row) as the correct answer, using the matrix form.
4. Go to preview mode and test different answers.
5. (Optional) add more detailed feedback/explanation to the exercise.

## Steps

### Step 1: create a new exercise with type "Math"

See an example below: ### Step 2: set the check-type in the main answer rule to "Parallel To"

Click on the "edit answers and specific feedback" button and change the relation for the main (i.e. first) answer rule to "Parallel to". ### Step 3: give a correct vector to check answers with

Give a vector as the correct answer in the answer box. This vector will be used to check whether the vectors given by learners are also correct by checking whether they are parallel.
To create a vector, use the matrix form and select the dimensions of your vector. Step 4: test different correct and incorrect answers

For our sample exercise a correct answer is the vector given by the creator or any vector which is the original vector multiplied by a non-zero scalar.
An example of a correct answer: And an incorrect answer for our sample exercise is any vector which is not parallel to the vector given by the creator. ### Step 5: add more detailed and specific feedback

Automatic feedback will be shown to student about whether they have the answer correct or incorrect including a correct answer.
However more detailed explanation on when answers are correct help the learners in learning from both their correct as incorrect answers.
You can add general feedback in the green "Detailed solution" box and orange "Question at wrong answer" box. For more specific feedback based on the characteristics of the student answer, check out the answer rules options.

## How does the Parallel to check work?

The method checks whether the difference between the given vector and the student answer differs by a constant value. One exception is added: if the constant is zero this is not seen as parallel. This prevents that the zero-vector answer is always seen as correct.

If the given vector to check against is a zero-vector, any vector of the same dimensions will be marked "Parallel to".

Do you want to know more about this check, whether you should use it for your exercise or any of the other checks? Please let us know via the chat icon in the right bottom of the screen!