Let R = AB

From A draw acr1 with r = R.

From B draw arc2 with r = R.

arc1 and arc2 meet at C.

From C draw arc3 with r = R.

arc3 and arc2 meet at D.

From D draw arc4 with r = R.

arc4 and arc2 meet at E.

E is on AB and EB = R.

From E draw arc5 wirg r = 2R.

arc1 and arc5 meet at F.

From F draw arc6 with r = R.

arc6 meets AB at M.

∆EFA ~ ∆FAM by AA.

They are both isosceles with same base angles.

∆EFA has 3 sides 2R, 2R, R.

∆EFA should have 3 sides R, R, R/2.