Determine m such that the two vectors 3i-9j and mi+2j are orthogonal?

possible answers


a. -2/3


b. -3/2


c. 4


d. 6

Determine m such that the two vectors 3i-9j and mi+2j are orthogonal?
If two vectors are orthoginal (i.e. perpendicular), their dot product is 0. This comes from the formula to find the angle formed by two vectors, which is cosθ = dot product/product of magnitudes. In order for θ=90, the cosine has to be 0, which means the dot product in that formula must be 0. Hence:


3m - 18 = 0


m = 6
Reply:Dot product must equal 0


3m - 18 = 0


m = 6


ANSWER d.
Reply:is that an error on the second vector: mi
Reply:If the vectors are orthogonal the dot product will be zero.





%26lt;3, -9%26gt; • %26lt;m, 2%26gt; = 3m - 18 = 0


3m = 18


m = 6





The answer is d.
Reply:if you have two arrays:


ai+bj and ci+dj


then the condition for them to be perpendicular is:


a*c+b*d=0


thus: 3*m+(-9)*2=0


m=6

quince