Factor $LaTeX: \displaystyle - 28 x^{3} - 40 x^{2} + 21 x + 30$ .

Factoring out the GCF $LaTeX: \displaystyle -1$ from each term gives $LaTeX: \displaystyle -(28 x^{3} + 40 x^{2} - 21 x - 30)$ . Grouping the first two terms and factoring out their GCF, $LaTeX: \displaystyle 4 x^{2}$ , gives $LaTeX: \displaystyle 4 x^{2}(7 x + 10)$ . Grouping the last two terms and factoring out their GCF, $LaTeX: \displaystyle -3$ , gives $LaTeX: \displaystyle -3(7 x + 10)$ . The polynomial now has a common binomial factor of $LaTeX: \displaystyle 7 x + 10$ . This gives $LaTeX: \displaystyle -1[4 x^{2} \left(7 x + 10\right) -3 \cdot \left(7 x + 10\right)] = -\left(7 x + 10\right) \left(4 x^{2} - 3\right)$ .