
Dot product and Angle
This is a question from calculus 3 class.
"Find the dot product of the vectors and the cosine of the angle between them."
u = i  3j + 7k
v = 8i  2j  2k
Okay, I get what to do, and I get answers but apparently they're wrong according to the back of the book. What am I doing wrong?
My work:
u dot v = (1*8) + (3*2) + (7*2) = 28 = dot product
u = sqrt(1^2 + (3)^2 + 7^2) = sqrt(59)
v = sqrt(8^2 + (2)^2 + (2)^2) = 6*sqrt(2)
(28) / ( sqrt(59) * (6*sqrt(2)) ) = .429601
cos^1 (.429601) = 1.12675 radians = angle
Edit: The book says the dot product is 0 and the angle is also 0.

(1*8) + (3*2) + (7*2) = 8 + 6  14 = 0.
If the book says that the angle is also 0, they're wrong. But if, as I suspect, they mean that the cosine of the angle is zero, they'd be correct.

Ahh I see.. I added 14 for some reason.. even though I went through this 3 times already. : I think I got the angle working too now.
Thanks! :)

No problem. Have a good one!