How do you factor #21x^3 - 28x#? Algebra Polynomials and Factoring Factoring Completely 1 Answer Nick F. Jul 5, 2016 #x = 0 or x = +-(2sqrt3)/3# Explanation: Start by taking out the common factor, 7x #7x(3x^2 - 4) = 0# #7x = 0 or 3x^2 - 4 = 0# #x = 0 or x^2 = 4/3# #x = 0 or x = +-2/sqrt3# #x = 0 or x = +-(2sqrt3)/3# Answer link Related questions What is Factoring Completely? How do you know when you have completely factored a polynomial? Which methods of factoring do you use to factor completely? How do you factor completely #2x^2-8#? Which method do you use to factor #3x(x-1)+4(x-1) #? What are the factors of #12x^3+12x^2+3x#? How do you find the two numbers by using the factoring method, if one number is seven more than... How do you factor #12c^2-75# completely? How do you factor #x^6-26x^3-27#? How do you factor #100x^2+180x+81#? See all questions in Factoring Completely Impact of this question 1549 views around the world You can reuse this answer Creative Commons License