Find the centre and radius of the sphere →r2−→r⋅(4→i+2→j−6→k)−11=0
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Solution
Let →r=x→i+y→j+z→k, r=√x2+y2+z2 ⇒r2=x2+y2+z2 ⇒→r⋅(4→i+2→j−6→k)=4x+2y−6z So, →r2−→r(4→i+2→j−6→k)−11=0 ⇒x2+y2+z2−4x−2y+6z−11=0 Comparing this equation with x2+y2+z2+2ux+2vy+2wz+d=0, we get
u=−2, v=−1, w=3 and d=−11 ∴ centre =(−u,−v,−w)=(2,1,−3) and