If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

## Precalculus (2018 edition)

### Course: Precalculus (2018 edition)>Unit 3

Lesson 2: Magnitude of vectors

# Vector magnitude from graph

Sal finds the magnitude of a vector given its graph.

## Want to join the conversation?

• why did he use double modulus for magnitude?
• Both single and double are common for vectors.
I have always used the double myself, as a reminder that the value inside is a vector/matrix.
Use what works for you, but if you use single, make sure it is obvious that your variable is not a scalar.
• what do the double lines outside of the "u" represents?? I know that if there is one line on each side of the variable, then it means absolute value. But, what do they represents if there are two lines on each side of the variable?
• Most of the time there are two bars on either side just to avoid confusion with the absolute value sign. In any case, if you are dealing with vectors and see the bars, it means magnitude.
• So to make this clearer for both me and everyone watching this, the magnitude of a vector is just its length? Why is it called magnitude and not just length?
• It's called magnitude because it doesn't always represent length. For example, the magnitude of a vector representing a car could be measured in feet travelled, or time spent, or MPH, or anything quantitative.
• Isn't it the square root of 58? Or did I do it wrong?
• Yes. He made a mistake. There's a note in the video if you don't have comments turned off.
• Speaking of magnitudes, in shouldn't magnitudes have units?
Like '√58' units? Because Sal says that the magnitude is basically the length of the vector. So shouldn't it it have units?
• My guess is that the units are not that important and doesn't affect the calculation, but when we're calculating the velocity of a car, for example, then units should be used since you want to know, is the car moving in km per hour or mile per hour?
• I always get stuck when I am making the lines on the graph for finding the points to find the magnitude of the vectors as I get confused in the DIRECTION in which i have to make the lines... So is their a specific method for this or not? I will be really pleased if my confusion is cleared.
• You can find the direction by observing where the head of the arrow of the vector is compared to the tail. For example, on a Cartesian plane, if the head is to the left of the tail, then the value of ∆x is negative, while if the head is to the right of the tail, the value of ∆x is positive. Similarly, if the head is below the the tail, the value of ∆y is negative, while the value of ∆y is positive if the head is above the tail. Maybe the previous practice problems and videos would help.
Hope this helps, and hope I didn't confuse you!
• At the value would be square root of 58.
• why are we putting double modulus signs for the vector magnitudes ?