-9x2 -7x +16 = 0
ax2 bx c = 0
a = -9
b = -7
c = 16
Δ = b2-4ac
Δ = -7² - (4 * -9 * 16)
Δ = 49 - (4*-144)
Δ = 49 - (-576)
Δ = 625 Δ > 0
-9x2-7x+16=0
x = -b ∓ √Δ 2a
x' = 7 - √625 2*-9 = 7 - 25.0 -18 = -18.0 -18 = 1.0
x" = 7 + √625 2*-9 = 7 + 25.0 -18 = 32.0 -18 = -1.77777777778
x' = 81.0
x" = -144.0
S = {x ∈ R / x' = 81.0, x" = -144.0 }