Question

If A= 21+31-k and B= 21-51+2k. Find A + B​

Answer 1

Explanation:

Consider the vector 

A=2i^+3j^−4k^

And B=5i^+2j^+4k^

Now, as we know

A.B=ABcosθ

θ is the angle between A and B

Therefore, 

cosθ=ABA.B

cosθ=22+32+(−4)252+22+42(2i^+3j^−4k^).(5i^+2j^+4k^)

=22+3

Answer 2

Answer:

Consider the vector  

A=2i^+3j^−4k^

And B=5i^+2j^+4k^

Now, as we know

A.B=ABcosθ

θ is the angle between A and B

Therefore,  

cosθ=ABA.B

cosθ=22+32+(−4)252+22+42(2i^+3j^−4k^).(5i^+2j^+4k^)

=22+3

25 is the ans