math
posted by dave .
Two vectors have magnitudes of 3 units and 8 units respectively. The resultant of these two vectors has a magnitude of 8 units. What is the angle between these two vectors?

make your sketch using the parallelogram property of vectors.
The resultant of 8 will be the diagonal of the quadrilateral with sides 3 and 8
let the angle opposite the resultant be Ø
by the cosine law:
8^2 = 8^2 + 3^2  2(8)(3)cos∏
48cosØ = 9
cosØ = 9/48
Ø = 79.163°
so by the gm property, the angle between the two vectors is
18079.163 = appr 100.8°