You can put this solution on YOUR website! this is a congruency within a single triangle MNP...since the congruency is order specific, it means that MN is congruent to PN (also as NP to NM) and PM is congruent to itself (MP)
this means that the two sides meeting at vertex N are congruent (equal)...a triangle with two equal sides is called (I know you know this) isosceles