The curve traced out by points P and P&nbstress; which lie on lines through a fixed point A where the midpoint M of PP&nbstress; is on a fixed line and the absolute value |PM| = the absolute value |P&nbstress;M| = the absolute value |MO|, where O is the projection of A onto that fixed line.
Origin of strophoidGreek strophos, twisted cord (from strephein, to turn; see streb(h)- in Indo-European roots) + –oid.
The equation for this strophoid is
x2(a + x)/(a − x).
- (geometry) A certain kind of curve.