Josel777 <josel777@hotmail.com> wrote: > Hello, > > I am trying to solve for A. > > (H/cos A )= (L/cos (A+B)) > > I know that cos (A+B)= cos A cos B - sin A sin B > > Substituting the previous into the original equation: > > H(cos A cos B - sin A sin B)= L cos A > > or > > H(cos A cos B)- H(sin A sin B)= L cos A > > What can I do after this? Divide through by cos A, giving H cos B - H tan A sin B = L I suspect you can do the rest. The last step will be to transform tan A = something into A = arctan(something), where arctan is the multivalued inverse tangent relation. David