This problem wasn't assigned to my class and is an even number so I wanted to make sure I was correct or even on the right track.

Is line through (4, 1, -1) and (2, 5, 3) perpendicular to the line through (-3, 2, 0) and (5, 1, 4)?

My solution:

A = < 2 - 4, 5 - 1, 3 - -1>

= <-2,4,4>

B = <5 - -3, 1 - 2, 4 - 0>

= <8,-1,4>

A X B = <20,40,-30>

<-2,4,4><20,40,-30> = 0

<8,-1,4><20,40,-30> = 0

They are perpendicular.