note that the zeroes should be x = 1 and x = - 2 not x = - 1 and x = 2
the factors are then ( x - 1 ) and (x + 2)
and x³ - 4x² - 7x + 10 = (x - 1 )(x + 2) = x² + x - 2
thus x² + x - 2 is a factor
dividing x³ - 4x² - 7x + 10 by x² + x - 2 gives x - 5
the third zero is x = 5
check : (5)³ -4(5)² - 7(5) + 10 = 125 - 100 - 35 + 10 = 0
They are opposites of each other.
-13.2 + 8.1 = -5.1
13.2 - 8.1 = 5.1
