-9x2 +2x +7 = 0
ax2 bx c = 0
a = -9
b = 2
c = 7
Δ = b2-4ac
Δ = 2² - (4 * -9 * 7)
Δ = 4 - (4*-63)
Δ = 4 - (-252)
Δ = 256 Δ > 0
-9x2+2x+7=0
x = -b ∓ √Δ 2a
x' = -2 - √256 2*-9 = -2 - 16.0 -18 = -18.0 -18 = 1.0
x" = -2 + √256 2*-9 = -2 + 16.0 -18 = 14.0 -18 = -0.777777777778
x' = 81.0
x" = -63.0
S = {x ∈ R / x' = 81.0, x" = -63.0 }