You can set Q(x, x, 2x).

QA=( 1-x，2-x，3-2x)，QB=(2-x， 1-x，2-2x)

QA * QB =( 1-x)(2-x)+(2-x)( 1-x)+(3-2x)(2-2x)

=6x？ - 16x+ 10

When x=4/3, there is a minimum value.

So the coordinate of Q is Q(4/3, 4/3, 8/3).

Have fun! I hope I can help you. If you don't understand, please ask. I wish you progress in your study! O(∩_∩)O