Abcdefgh is a regular octagon. M is a point on the line dh. N is a point on the line fm. The line dn and fm are perpendicular. Prove that triangles fhm and dfp are congruent

ΔFHM and ΔDFP by addition to ΔMOF and ΔPDO respectively gives
ΔHOP and ΔDOF, which are congruent.
Response:
Based on the properties of a regular octagon, the diagonals DH and BF
of a regular octagon are perpendicular, and they bisect each other,
given that the length of half the diagonal represent the radius of the
circumscribing circle.
Therefore;
∠NFP ≅ ∠NFP by reflexive property
∠PNF ≅ ∠MOF all right angles are congruent
ΔMOF is similar to ΔPNF by Angle-Angle AA similarity postulate.
∠OMF ≅ ∠DMN by reflexive property
Therefore;
ΔDMN is similar to ΔMOF by AA similarity postulate.
Similarly, we have;
ΔDMN ~ ΔPDO by AA similarity postulate;
Therefore;
ΔPDO is similar to ΔOMF by transitive property
∠ODP ≅ ∠OFM by CASTC, Corresponding Angles of Similar Triangle are Congruent.
OD = OF distance from center to the vertex of a regular octagon are
equal to the radial length of the circumscribing circle and are therefore
equal.
Therefore;
ΔPDO ≅ ΔOMF by Angle-Side-Angle ASA congruency rule
ΔPDO = ΔOMF definition of congruency
ΔHOF = ΔDOF
ΔFHM = ΔHOF - ΔOMF subtraction property
Similarly
ΔDFP = ΔDOF - ΔPDO = ΔHOF - ΔOMF = ΔFHM by substitution property
ΔDFP = ΔFHM
ΔFHM = ΔDFP by symmetric property.
Therefore;
Learn more about the properties of a regular octagon here:
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