Orthocentre of triangle

If A(0,2,3) , B=(2,-1,5) are two vertices of triangle ABC whose orthocentre is H . Then distance between the orthocentres of triangle HAC and triangle HBC is

If the centroid and orthocentre of a triangle are (3,3) and (-3,5) respectively then the circumcentre is

Orthocentre of a triangle whose vertex are (8,-2),(2,-2) and (8,6) is

If O is the orthocentre of a triangle ABC and angleBOC=100^(@) , the measure of angleBAC is

If the distance between centroid and orthocentre of a triangle is 12 cm then find the distance between its orthocentre and circumcentre.

If O is the circumcentre,G is the centroid and O' is orthocentre or triangle ABC then prove that: vec OA+vec OB+vec OC=vec OO