The intersection of the spheres x2+y2+z2+7x−2y−z=13 and x2+y2+z2−3x+3y+4z=8 same as the intersection of one of the spheres and the plane
x-y-z=1
x-2y-z=1
x-y-2z=1
2x-y-z=1
The given spheres are
x2+y2+z2+7x−2y−z=13--------(i)
and x2+y2+z2−3x+3y+4z=8------(ii)
Subtracting (ii) from (i), we get
10x−5y−5z−5=0or 2x−y−z=1