Question

Find the angle between the vectors a=i+j+k and b=-i-j+2k

Answer 1

Explanation:

Here a.b=(-1*1)+(-1*1)+(2*1)

i.e a.b=0

Now

a.b=|a|.|b| cosα

Cosα=0

α=90°

I think this is the answer....

Answer 2

Use,

a.b= |a| |b| cos theta

Cos theta= a.b/|a| |b|

Then find the dot product and the magnitude of the vectors

The answer will be 90 degrees