If $x+1$ is a factor of the polynomial $2x^2+kx$,then the value of $k$ is

Is the following expression a polynomial? Justify your answer:
$\sqrt{3} x^{2}-2 x$

Factorise the following quadratic polynomial by splitting the middle term:
$15x^2 + 7x - 2$

Prove that $(a+b+c)^{3}-a^{3}-b^{3}-c^{3}=3(a+b)(b+c)(c+a).$

Which one of the following is a polynomial?

Which of the following expressions is a polynomial? State the reason. If an expression is a polynomial,state whether it is a polynomial in one variable or not: $\sqrt{3} x^{2}+\pi x-9$