Factor $LaTeX: \displaystyle 90 x^{3} + 70 x^{2} + 27 x + 21$ .

Grouping the first two terms and factoring out their GCF, $LaTeX: \displaystyle 10 x^{2}$ , gives $LaTeX: \displaystyle 10 x^{2}(9 x + 7)$ . Grouping the last two terms and factoring out their GCF, $LaTeX: \displaystyle 3$ , gives $LaTeX: \displaystyle 3(9 x + 7)$ . The polynomial now has a common binomial factor of $LaTeX: \displaystyle 9 x + 7$ . This gives $LaTeX: \displaystyle 10 x^{2} \left(9 x + 7\right) +3 \cdot \left(9 x + 7\right) = \left(9 x + 7\right) \left(10 x^{2} + 3\right)$ .