November 25, 2015

Homework Help: Physics

Posted by Jamie on Friday, October 6, 2006 at 5:02pm.

Use the definition of scalar product( vector A* vector B = abcos theda and the fact that vector A * vector B = axbx+ ayby+azbz to calculate the angle between the two vectorgiven by vector A= 3i + 3j + 3k and vector B= 2i + 1j + 3k.

The book said the answer is 22 degreess but I can figure out how to get 22 degrees can you help me?

The magnitude of AdotB is sqrt (9+9+9)sqrt(4+1+9)=sqrt (27*14)=19.44
but the dot product is then 19.44*cosTheta

Now, the dot product is equal to (from vector notation i*i + j*j + k*k

(3*2 + 3*1 + 3*3)

Set this equal to 19.44cosTheta, and solve for cos Theta.

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