Ask Questions, Get Answers

Want to ask us a question? Click here
Browse Questions
Home  >>  TN XII Math  >>  Vector Algebra
0 votes

If the sum of two unit vectors is a unit vector prove that the magnitude of their difference is $\sqrt{3}$.

Can you answer this question?

1 Answer

0 votes
  • For any two vectors $ \hat a \: and \: \hat b$ $(\hat a + \hat b)^2=(\hat a)^2+2\hat a.\hat b+(\hat b)^2=a^2+2\hat a.\hat b+b^2$ $(\hat a-\hat b)^2=a^2-2\hat a.\hat b+b^2$ $(\hat a+\hat b).(\hat a-\hat b)=a^2-b^2$
Step 1
$ \hat a \: and \: \hat b$ are unit vectors with $ \hat a +\hat b=\hat c$ also a unit vector.
Step 2
$ | \hat a+\hat b|^2=|\hat c|^2=\hat a^2+2\hat a.\hat b+\hat b^2$
$ \therefore 1= 1+(1)(1) \cos\theta+1$
or $ \cos\theta = \large\frac{-1}{2}$
Step 3
Now $ |\hat a-\hat b|^2 = \hat a^2-2\hat a.\hat b+\hat b^2$
$ = 1-2(1)(1) \cos\theta+1$
$ = 2-2 \bigg( -\large\frac{1}{2} \bigg) = 2+1=3$
$ \therefore | \hat a-\hat b|= \sqrt 3$
answered Jun 1, 2013 by thanvigandhi_1

Related questions

Ask Question
student study plans
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App