Identities of cos

  • Thread starter bob4000
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  • #1
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i and the rest of my class are finding it impossible to find the answer to this part of the question:

find the exact value of cos A from secA-cosA=1/2

thanks in advance
 

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  • #2
dextercioby
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Make the substitution [itex] \cos A =x [/itex], then the definition of secant and in the end you should get a quadratic equation in "x".

Daniel.
 
  • #3
finchie_88
What you do is that you multiply everything by cosA, so that you get a quadratic, and then solve that in terms of cosA, to get A, simply inverse cos it, eg

(1/cosA) - cosA = 1/2
-cos^2A + 1 = (1/2)cosA
0 = cos^2A + 0.5cosA -1
Then solve with the quadratic formula:biggrin:

edit: dam,beaten to it...
 
  • #4
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merci beaucoup
 

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