You are Here: Home >< Maths

# vectors

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
1. Why is this wrong... ??
Attached Images

2. (Original post by pippabethan)
Why is this wrong... ??
It's not wrong, you've just found the obtuse angle between the two lines, the question wants the acute angle.
3. (Original post by Zacken)
It's not wrong, you've just found the obtuse angle between the two lines, the question wants the acute angle.
Now that was a quick response.
4. (Original post by Zacken)
It's not wrong, you've just found the obtuse angle between the two lines, the question wants the acute angle.
Okay, thank you! I was worried I didn't understand it properly! How do I 'translate' this into the angle they want?
5. (Original post by pippabethan)
Okay, thank you! I was worried I didn't understand it properly! How do I 'translate' this into the angle they want?
Well, you have and you know is obtuse, so you really want
6. (Original post by Zacken)
Well, you have and you know is obtuse, so you really want
Thank you so much! I (eventually) got there! Just to speed up my working in the exam, is there a slightly different way I could approach this to obtain the acute angle originally?
7. (Original post by pippabethan)
Thank you so much! I (eventually) got there! Just to speed up my working in the exam, is there a slightly different way I could approach this to obtain the acute angle originally?
Not really. Unless you could see that if you took AB and AC and their dot product was negative. Then you can use BA and AC or AB and CA to get a positive dot product.
8. (Original post by Zacken)
Not really. Unless you could see that if you took AB and AC and their dot product was negative. Then you can use BA and AC or AB and CA to get a positive dot product.
Ah right, I might try that in the future

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 21, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams