Question: the resultant of two vectors a and b is perpendicular?
Answer: Figure given above explains the answer. Given, result vector of a and b is perpendicular to a and its magnitude is half of b. ... since required angle is angle between two vector are in same plane which is 180-c. hence using sinc=mag(resultant/vector b)=b/2/b=1/2,c=30,hence 180-c=180–30=150 ans.