Question

Which shows one way to determine the factors of x3 – 9x2 + 5x – 45 by grouping?

x2(x – 9) – 5(x – 9)
x2(x + 9) – 5(x + 9)
x(x2 + 5) – 9(x2 + 5)
x(x2 – 5) – 9(x2 – 5)

Answer 1

x³ - 9x² + 5x - 45

x²(x - 9) - 5(x - 9) ⇒ x³ - 9x² - 5x + 45 INCORRECT
x²(x + 9) - 5(x + 9) ⇒ x³ + 9x² - 5x - 45 INCORRECT

x(x² + 5) - 9(x² + 5) ⇒ x³ + 5x - 9x² - 45 CORRECT
It just needs to be rearranged.

x(x² - 5) - 9(x² - 5) ⇒ x³ - 5x - 9x² + 45 INCORRECT