Question about Articles in S. L. Looney book "Plane Trig

[KarimTef]

S. L. Looney in his book "Plane geometry", when he writes a formula, he notes next to it it's Article number. Example:

In page 11: cos (A + B) = cos A cos B - sin A sin B (Art. 88)

What are these articles? If they are gathered in a free downloadable document, I would like to have it.

Thank you.

[Guest]

It simply refers to a later (or earlier) section of the same book. If you go to the section labelled 88 in the book he gives a proof of the formula.

Hope this helped,

R. Baber.

[KarimTef]

@Baber: Thank you very much.