5x2 +21x +16 = 0
ax2 bx c = 0
a = 5
b = 21
c = 16
Δ = b2-4ac
Δ = 21² - (4 * 5 * 16)
Δ = 441 - (4*80)
Δ = 441 - (320)
Δ = 121 Δ > 0
5x2+21x+16=0
x = -b ∓ √Δ 2a
x' = -21 - √121 2*5 = -21 - 11.0 10 = -32.0 10 = -3.2
x" = -21 + √121 2*5 = -21 + 11.0 10 = -10.0 10 = -1.0
x' = -80.0
x" = -25.0
S = {x ∈ R / x' = -80.0, x" = -25.0 }