Nov 13, 2012 Thread starter #1 B Bushy Member Jul 2, 2012 40 In square ABCD need to show $cos a = \frac{1}{12}$ Attachments untitled.JPG 10.1 KB Views: 16

Nov 13, 2012 Admin #2 M 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.

While I haven't worked this problem yet, I am thinking the law of cosines may help, along with the relationship between supplementary angles.

Nov 13, 2012 #3 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 $\cos a$.

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 $\cos a$.