Vectors help

I'm having problems with this question mainly because I can't picture what the parallelogram looks like so if someone can help me picture it, then I think I can solve the problem, thanks.

The vectors AB(with an arrow above from left to right) and AC(also with an arrow above from left to right) are (-1, 0, 3) and (2, 4, 3) respectively. The vector AD(again with the same arrow) is the sum of AB and AC. Determine the acute angle, in degrees correct to one decimal place, between the diagonals of the parallelogram defined by the points A, B, C and D.

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It's unusual that ABCD do not go in order around the parallelogram, but that does seem correct.

The angles you've worked out are between one of the diagonals and one of the sides.

Aside: You have worked out AD.AB, giving you the angle BAD(!) as 42 degrees, but you've labelled angle BDA as 42. Also you're asked to quote to 1 dec. pl.


You need to look at the angle between the two diagonals, AD and BC.

PS: I've not checked the arithmetic, and assumed that's correct.