An altitude is a perpendicular dropped from the vertex to the opposite side.

 

Orthocentre is a point where the 3 altitudes dropped from 3 vetices of the triangle meet.

 

Median is the line that joins the mid point of the side to the opposite vertex ...

 

Incenter is the point where the angle bisectors of the three angles meet ..

 

Circumcenter is point where perpendicular bisectors of the 3 lines meet ..

 

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