Q.

A plane meets the coordinate axes in points A, B, C and the centroid of the triangle ABC is (α,β,γ). The equation of the plane is:

1 xα+yβ+zγ=3  
2 αx+βy+γy=3αβγ  
3 xα+yβ+zγ=12  
4 None of these  

Ans.

(1)

Ans.    xα+yβ+zγ=3

Explanation:

Let the equation of the required plane be

            xa+yb+zc=1                         ...(i)

It meets coordinate axes in points

            A(a,0,0),  B(0,b,0),  C(0,0,c)

The centroid of ∆ABC is (a3,b3,c3)

⇒                     a3=α,  b3=β,  c3=γ

⇒                       a=3α,  b=3β,  c=3γ

Hence, the required plane is

                               x3α+y3β+z3γ=1

i.e.,                                 xα+yβ+zγ=3