physics vectors?

Question

Vector A has components
Ax = -5.1; Ay = 5.3; Az = 2.3;
while vector B has components
Bx = 7.3; By = -7; Bz = 4.9.
What is the angle thetaAB between these vectors?
(Answer between 0 and 180 degrees.) Answer in units of degrees.

Answer 1

Lets continue what meg started. Thus dot product
p=-5.1*7.3 + 5.3*(-7) + 2.3*4.9 = -63.06 and
p=|A|*|B|*cos(t) = sqrt(5.1^2 + 5.3^2 + 2.3^2) * sqrt(7.3^2 + 7^2 + 4.9^2) * cos(t) = 86.60807*cos(t);
thus cos(t) = -63.06/86.60807, hence
t = 2.386354 / 3.14159265 * 180 = 136°44’

Answer 2

Use the formula for the dot product
A dot B= abs(A) abs(B) cos (angle)
where A dot B =AxBx+AyBy+AzBz

Answer 3

Use the formula for the dot product
A dot B= abs(A) abs(B) cos (angle)
where A dot B =AxBx+AyBy+AzBz