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?