Step 1 :Given the polynomial \(9x^{4} + 21x^{3} - 9x^{2} - 21x\), we are asked to factor it completely.
Step 2 :Factoring out the common factor of 3x, we get \(3x(3x^{3} + 7x^{2} - 3x - 7)\).
Step 3 :Next, we factor the cubic polynomial inside the parentheses. We can do this by grouping the terms and factoring out common factors. This gives us \(3x((x - 1)(3x^{2} + 7x + 3))\).
Step 4 :Finally, we factor the quadratic polynomial inside the parentheses. This gives us \(3x(x - 1)(x + 1)(3x + 7)\).
Step 5 :Comparing this with the given options, we see that it matches with option c.
Step 6 :So, the correct answer is option c.