Answer:
x = - 2 , x = 7
Explanation:
to find the zeros let y = 0 , then
3x² - 15x - 42 = 0 ( divide through by 3 )
x² - 5x - 14 = 0
consider the factors of the constant term (- 14) which sum to give the coefficient of the x- term (- 5)
the factors are + 2 and - 7 , since
2 × - 7 = - 14 and 2 - 7 = - 5 , then
(x + 2)(x - 7) = 0
equate each factor to zero and solve for x
x + 2 = 0 ⇒ x = - 2
x - 7 = 0 ⇒ x = 7