Posted by **dave** on Friday, March 1, 2013 at 6:58pm.

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?

- math -
**Reiny**, Friday, March 1, 2013 at 8:04pm
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

180-79.163 = appr 100.8°

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