-15x2 +2x +13 = 0
ax2 bx c = 0
a = -15
b = 2
c = 13
Δ = b2-4ac
Δ = 2² - (4 * -15 * 13)
Δ = 4 - (4*-195)
Δ = 4 - (-780)
Δ = 784 Δ > 0
-15x2+2x+13=0
x = -b ∓ √Δ 2a
x' = -2 - √784 2*-15 = -2 - 28.0 -30 = -30.0 -30 = 1.0
x" = -2 + √784 2*-15 = -2 + 28.0 -30 = 26.0 -30 = -0.866666666667
x' = 225.0
x" = -195.0
S = {x ∈ R / x' = 225.0, x" = -195.0 }