Explanation:
the equation is
2x² + 3x - 8 = 0
the generic solution to such a quadratic equation is
x = (-b ± sqrt(b² - 4ac))/(2a)
in our case
a = 2
b = 3
c = -8
x = (-3 ± sqrt(9 - 4×2×-8))/(2×2) =
= (-3 ± sqrt(9 + 64))/4 = (-3 ± sqrt(73))/4
x1 = (-3 + sqrt(73))/4 = (-3 + 8.544003745)/4 =
= 1.386000936... ≈ 1.39
x2 = (-3 - sqrt(73))/4
but that would negative, and therefore not a wanted solution.
x ≈ 1.39
is the targeted solution.