Question

if the resultant of the vector 3i +4j +5k and 5i +3j +4k makes angle theeta with x axis then find cos theeta

Answer 1

The given vectors A and B are 3i +4j +5k and 5i +3j +4k respectively.  The sum of A and B is 8i +j –k.

The subtraction of A and B is -2i +7j -9k. Then consider A+B = C and A - B = D.

Then cos(theta) is A·B/|A||B|. A·B= 0. The answer of cos(theta) is 0. Finally, the theta is 90°.