the proof that there are only five equable triangles (integer sided) was done in 1904
this version of a proof is largely due to David Wells with small bits of help from me
it is complex but involves only GCSE tools
roof truss
one roof making company calls the various truss designs:
Howe truss
Fink truss
Attic truss
which one uses most wood?
quite long and complex calculations involving the sine and cosine rule
symmetry is assumed
the Fink truss does not have struts that are perpendicular to the main, 6m lengths (even though it looks like they might be)
cosine rule
