Question

pls anyone solve this

Answer 1

Here is the solution. [correct one]

For two vectors A nad B
$cos \beta = \frac{A * B}{|A||B|}$
where β is the angle between the two vectors

Now for given two vectors
$cos \beta = \frac{(2i+3j-4k) * (-i+2j+k)}{ \sqrt{ 2^{2} + 3^{2} + (-4)^{2} } \sqrt{ (-1)^{2} + 2^{2} + 1^{2} } }$
$cos \beta = \frac{-2+6-4}{ \sqrt{ 2^{2} + 3^{2} + (-4)^{2} } \sqrt{ (-1)^{2} + 2^{2} + 1^{2} } }$
$cos \beta = \frac{0}{ \sqrt{ 2^{2} + 3^{2} + (-4)^{2} } \sqrt{ (-1)^{2} + 2^{2} + 1^{2} } } =0$

So,
$\beta =90 degree = \frac{ \pi }{2}$
That means 
n=1

#Prashant24IITBHU

Answer 2

n = 2 is the right answer