Expand the following expression: -5x(x-7)(x+3)

Expansion of the given expression will result in x to the 3rd power, as there are 3 parts involving x, multiplied together. Let's ignore -5x for a second, and multiply the two expressions in brackets (using expansion rules of (a+b)(c+d) = ac + ad +bc +bd);
-5x(x-7)(x+3) = -5x(x^2 +3x - 7x -(7*3)) = -5x(x^2 -4x - 21).
We can now multiply each unit in the bracket by -5x, to get the final expression; (-5x * x^2) + (-5x * (-4x))  + (-5x * (-21)) = -5x^3 + 20x^2 + 105x

So the final answer is -5x^3 + 20x^2 + 105x