# Vector help

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• Mar 20th 2011, 01:49 PM
mathsnub
Vector help
Hi all,

Struggling with three vector questions and would appreciate if someone could help me.

http://i55.tinypic.com/2ymvsqw.png
The roof is symmetrical :)

Determine the vectors AB, BC and CA and in each case calculate the modulus.
Find the direction cosines of AB and hence calculate the angle (correct to 1 decimal place) between AB and each of the positive coordinate axes

Find all the angles (in degrees) in the triangle MDF, correct to 2 decimal places.

Obtain the outward unit normal vector to the sloping roof FGHC

Would really appreciate it (Hi)
• Mar 20th 2011, 02:14 PM
dwsmith
Quote:

Originally Posted by mathsnub

Obtain the outward unit normal vector to the sloping roof FGHC

The cross product of HG and GF will allow you to obtain a normal vector to the region.
• Mar 20th 2011, 02:18 PM
dwsmith
Quote:

Originally Posted by mathsnub

Find all the angles (in degrees) in the triangle MDF, correct to 2 decimal places.

M(0,7,3.5), D(6,12,0) and F(3,0,8.5)

Graph these points in 3D and solve for the angles.

To determine all the vectors, make point O the origin like I did hear and determine the vectors and modulus will come easily.