Scalar product to find angle between two vectors

[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

AdotB=(6.63)(7.81)cosΘ

Θ=acos(38/51.78)

Θ=42.79=WRONG

 

[genneth]

Check your arithmetic.

 

[noeinstein]

I went over it again and got the same answer.

 

[genneth]

Then why do you think it's wrong?

 

[noeinstein]

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

 

[genneth]

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

 

[noeinstein]

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

 

[noeinstein]

:d.. dah