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Trigonometry Triangle question

Bushy

Member
Jul 2, 2012
40
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In square ABCD need to show $cos a = \frac{1}{12}$
 

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MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
While I haven't worked this problem yet, I am thinking the law of cosines may help, along with the relationship between supplementary angles.
 

Fantini

"Read Euler, read Euler." - Laplace
MHB Math Helper
Feb 29, 2012
342
I gave it some thought, and I believe applying law of cosines twice will do the trick. First you apply to the triangle $AEC$ to find side $EC$, and then apply it to the triangle $CED$ to find $\cos a$.