-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 = -32.0 -18 = 1.77777777778
x" = -7 + √625 2*-9 = -7 + 25.0 -18 = 18.0 -18 = -1.0
x' = 144.0
x" = -81.0
S = {x ∈ R / x' = 144.0, x" = -81.0 }