Rewrite these two facts as a polynomial: the two zeroes of a certain quadratic add up to −4 and multiply to −21. Taking the leading coefficient as 1, the polynomial is:

A quadratic with zeroes $\alpha ,\beta$ is $x^2-(\alpha +\beta )x+\alpha \beta$. Here $x^2-(-4)x+(-21)=x^2+4x-21$. (Check with the zeroes 3 and −7: they add to −4 and multiply to −21.) The option $x^2-4x-21$ copies the sum in without the minus sign of $-(\alpha +\beta )$; $x^2+4x+21$ flips the sign of the product; $x^2-21x-4$ swaps the sum and the product.