Answer:
3 (7 a - 5) (a - 2)
Explanation:
Factor the following:
21 a^2 - 57 a + 30
Factor 3 out of 21 a^2 - 57 a + 30:
3 (7 a^2 - 19 a + 10)
Factor the quadratic 7 a^2 - 19 a + 10. The coefficient of a^2 is 7 and the constant term is 10. The product of 7 and 10 is 70. The factors of 70 which sum to -19 are -5 and -14. So 7 a^2 - 19 a + 10 = 7 a^2 - 14 a - 5 a + 10 = a (7 a - 5) - 2 (7 a - 5):
3 a (7 a - 5) - 2 (7 a - 5)
Factor 7 a - 5 from a (7 a - 5) - 2 (7 a - 5):
Answer: 3 (7 a - 5) (a - 2)