If $$(1/x) + (1/y) + (1/z) = 0$$ and $$x + y + z = 11$$, then what is the value of $$x^{3}+y^{3}+z^{3}-3xyz$$ ?
Given : $$\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=0$$
=> $$\frac{yz+zx+xy}{xyz}=0$$
=> $$xy+yz+zx=0$$ -------------(i)
Also, $$x+y+z=11$$ ------------(ii)
Squaring both sides, we get :
=> $$(x+y+z)^2=(11)^2$$
=> $$(x^2+y^2+z^2)+2(xy+yz+zx)=121$$
Substituting value from equation (i),Â
=> $$x^2+y^2+z^2=121$$ ------------(iii)
To find : $$x^{3}+y^{3}+z^{3}-3xyz$$Â
= $$(x+y+z)[(x^2+y^2+z^2)-(xy+yz+zx)]$$
Substituting values from equations (i), (ii) and (iii),
= $$(11)(121-0)$$
= $$11\times121=1331$$
=> Ans - (A)
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