Answer:
(7x - 2)(3x^2 - 4)
See below.
Explanation:
21x^3 - 9x^2 - 28x + 12
3x^2(7x - 3) - 4(7x - 3)
The common factor in this is 7x - 3. Use the distributive property to bring it out.
(7x - 3) [(3x^2 ) - 4]
(7x - 3)(3x^2 - 4)
You could factor 3x^2 - 4 but most times, since you can't reduce this to an integer result, you just leave it as it is.
If you have to use surds then the answer could be
(7x - 3)(√3 - 2)(√3 + 2)