Explanation:
the formula to find the x values to deliver y=0 results of a squared equation is
x = (-b ± sqrt(b² - 4ac))/(2a)
a, b, c are the constant factors in the 3 terms of a squared equation.
here in our example of 2x² - x - 10
a = 2
b = -1
c = -10
x = (1 ± sqrt(1² - 4×2×-10))/(2×2) =
= (1 ± sqrt(1 + 80))/4 = (1 ± sqrt(81))/4 =
= (1 ± 9)/4
x1 = (1 + 9)/4 = 10/4 = 2 2/4 = 2 1/2 = 2.5
x2 = (1 - 9)/4 = -8/4 = -2