If a triangle ABC has vertices A(-1,7),B(-7,1),C(5,-5) then its orthocentre has coordinates:

Vertices of the given triangle are A(-1,7),B(-7,1),C(5,-5) Observing the points, the vertices are at equal distances from origin, so that the circumcentre of the  triangle is S(0,0)The centroid of the triangle is G=x1+x2+x33,y1+y2+y33=−1−7+53,7+1−53=−1,1 In any triangle G divides OS in the ratio 2:1 internally It implies O=3G−2S=−3,3