$證明：? (1)?∵?∠BEM+∠NEC= 135°，??∠BEM +∠BME= 135°?$
$∴?∠BME= ∠CEN?$
$∵?∠B=∠C?$
$∴?△BEM ∽△CNE?$
$?(2)△BEM∽△ENM?或?△CNE∽△ENM?$
$與?(1)?同理?△BEM∽△CNE?$
$∴?\frac {BE}{CN}=\frac {EM}{NE}?$
$又∵?BE=EC?$
$∴?\frac {EC}{CN}=\frac {EM}{NE}?$
$∴?\frac {EC}{EM}=\frac {CN}{NE}?$
$又∵?∠ECN=∠MEN=45°?$
$∴?△ECN∽△MEN?$
