• Support PF! Buy your school textbooks, materials and every day products via PF Here!

I stuck at this vector question

  • Thread starter Greychu
  • Start date
If A = 5ax + 3ay + 2az
B = -ax + 4ay + 6az
C = 8ax + 2ay

Find the value of m and n such that mA + nB + C is parallel to y-axis.

My problem is I did not know how to determine the m and n value because I did not know what method can use to solve for mA + nB + C parallel to y axis. Does it means that the vector line of mA + nB + C must be a straight line parallel to y axis?

mA + nB + C
= (5m - n + 8)ax + (3m + 4n + 2)ay + (2m + 6n)az

To use dot product means that (mA + nB + C) dot (??) = 1
cross product means that (mA + nB + C) cross (??) = 0

I dunno the ?? is stand for what.... can someone pls help me?
mA + nB + C should be a vector that should have same direction as <0,1,0>.

What that means is that other than y component not equals zero, x and z components should be zero.
Thanks, now I am able to solve the question :D

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving