The distance between the points  5,1,7and  c,−5,1 is  9 then c=

The distance between two points  Ax1,y1,z1and Bx2,y2,z2 is d=x2−x12+y2−y12+z2−z12Hence the distance between the points   5,1,7and c,−5,1  is d=c−52+36+36It implies that   9=c−52+36+3681=c−52+72c−52=9c=5±3=8,2          Therefore,  c=8,2