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2. Polynomials
hard
If $x+y+z=0,$ show that $x^{3}+y^{3}+z^{3}=3 x y z$.
Option A
Option B
Option C
Option D
Solution
Since $x+y+z=0 $ $\therefore x+y=-z$
or $(x+y)^{3}=(-z)^{3}$ or $x^{3}+y^{3}+3 x y(x+y)=-z^{3}$
or $x^{3}+y^{3}+3 x y(-z)=-z^{3}$ $[\because x+y=(-z)]$
or $x^{3}+y^{3}-3 x y z=-z^{3}$ or $\left(x^{3}+y^{3}+z^{3}\right)-3 x y z=0$
or $\left(x^{3}+y^{3}+z^{3}\right)=3 x y z$
Hence, if $x+y+z=0,$ then $\left(x^{3}+y^{3}+z^{3}\right)=3 x y z$
Standard 9
Mathematics