Scalar product to find angle between two vectors

1. Sep 16, 2007

noeinstein

Use the definition of scalar product, a·b = ab cos , and the fact that a·b = axbx + ayby + azbz (see Problem 46) to calculate the angle between the two vectors given by a = 2.0 i + 6.0 j + 2.0 k and b = 4.0 i + 3.0 j + 6.0 k.

AdotB= 8i + 18j + 12k

A=sqrt(2^2 + 6^2 + 2^2)=6.63
B=sqrt(4^2 + 3^2 + 6^2)=7.81

Θ=acos(38/51.78)

Θ=42.79=WRONG

2. Sep 16, 2007

genneth

3. Sep 16, 2007

noeinstein

I went over it again and got the same answer.

4. Sep 16, 2007

genneth

Then why do you think it's wrong?

5. Sep 16, 2007

noeinstein

because the online assignment is giving me a big fat red X. lol

6. Sep 16, 2007

genneth

Then I'll admit to making whatever mistake you've apparently made. :D

7. Sep 16, 2007

noeinstein

Never mind. Got it. I switched the values of ay and by. Thanks.

8. Sep 16, 2007

:d.. dah