X²+10x=39 maka nilai x adalah

x^2 + 10x = 39
x^2 + 10x -39 = 0
(x + 13)(x - 3) = 0
x = -13 atau x = 3

Persamaan Kuadrat.

x² + 10x - 39 = 0
a = 1, b = 10, c = -39
x₁₂ = [-b ± √(b² - 4ac)] / (2a)
      = {-10 ± √[10² - 4(1)(-39)]| / [2(1)]
x₁ = (-10 + 16) / 2 = 3
x₂ = (-10 - 16) / 2 = -13
x = 3 atau x = -13