I am trying to teach myself AS maths. This is from Introducing mechanics a txt book by Jefferson and Beadsworth. exercise 2C question 1 part vi)(adsbygoogle = window.adsbygoogle || []).push({});

Question given vectorb=6i-3j-2k;

|b| is established as = 7 by calculation

Question

Calculate the angles between b and positive x-, y- and z- directions.

My answer: these are

sine alpha =6/7 = 59 degrees - subtract from 180 to give angle from z axis

Sine beta =2/7 = 16.6 degrees - this is angle from x axis

Sine theta = 3/7 = 25.4 degrees. Need to add 90 degrees to give angle from y axis.

However these are not the correct answers. The correct answers appear to be cosines of the above. This does not make sense to me can you expalin?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Vectors in three dimensions

**Physics Forums | Science Articles, Homework Help, Discussion**