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paper 2 2005 - HSN forum

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paper 2 2005


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#1 laura_lou92

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Posted 20 May 2009 - 03:51 PM

Vectors a and c are represented by two sides of an equilateral triangle with sides length 3units.

Vector b is 2units long and b is perpendicular to both a and c.

Evaluate the scalar product a.(a+b+c).

Any help would be muchly appreciated =)

#2 SncZ

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Posted 20 May 2009 - 04:24 PM

so a.(a+b+c) can be expanded to a.a + a.b + a.c

a.a = |a||a|cos(0) = |a||a| .
a=3, so a.a = 3x3 =9

a.b and a.c can be done similarly.

once you have a.a , a.b and a.c just add them all up smile.gif

hope this helped biggrin.gif



( you should end up with 9 + 0 + 9/2 = 27/2 )





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