# Math Help - Vectors!! Trouble

1. ## Vectors!! Trouble

Find the value of c such that,for all real x, the vectors cxI -6J +3K and xI +2J +2cxK make an obtuse angle with each other

I means unit vector along x-axis!!

2. ## Re: Vectors!! Trouble

Hi
Have you tried the dot product ?

3. ## Re: Vectors!! Trouble

Originally Posted by grgrsanjay
Find the value of c such that,for all real x, the vectors cxI -6J +3K and xI +2J +2cxK make an obtuse angle with each other
First: please review this post. Have you written it correctly?

Second: Two vectors form an obtuse angle if and only if their dot product is negative.

4. ## Re: Vectors!! Trouble

The vectors can form obtuse angle when Dot product is less than Zero...Thats it??
Or is there any other condition??

I get cx^2 - 12 + 6cx < 0,

Then how should i proceed...c value must satisfy for all real x