-9x2 +16x -7 = 0
ax2 bx c = 0
a = -9
b = 16
c = -7
Δ = b2-4ac
Δ = 16² - (4 * -9 * -7)
Δ = 256 - (4*63)
Δ = 256 - (252)
Δ = 4 Δ > 0
-9x2+16x-7=0
x = -b ∓ √Δ 2a
x' = -16 - √4 2*-9 = -16 - 2.0 -18 = -18.0 -18 = 1.0
x" = -16 + √4 2*-9 = -16 + 2.0 -18 = -14.0 -18 = 0.777777777778
x' = 81.0
x" = 63.0
S = {x ∈ R / x' = 81.0, x" = 63.0 }