Question

resolva as equaçoes do 2 grau b)x2-x-20=0 c)x2-3x-4=0 d)x2-8x+7=0

Answer 1

x² - x -20 = 0

Δ = b² - 4.a.c
Δ = -(-1)² - 4.1.(-20)
Δ = 1 + 80
Δ = 81

X = $\frac{-(-1) +- \sqrt{81} }{2.1}$
X = $\frac{-(-1) +- 9}{2}$
X = $\frac{1+9}{2}$
X = 5

X = $\frac{1-9}{2}$
X = 4

S{4,5}.

x² - 3x -4 = 0

Δ = -3² - 4.1.(-4)
Δ = 9 + 16
Δ = 25

X = $\frac{-(-3) +- \sqrt{25} }{2}$
X = $\frac{-(-3)+- 5}{2}$
X = $\frac{3+5}{2}$
X = 4

X = $\frac{3 - 5}{2}$
X = -1

S{4,-1}.

x² -8x +7 = 0

Δ = -8² -4.1.7
Δ = 64 - 28
Δ = 36

X = $\frac{-(-8)+- \sqrt{36} }{2}$
X = $\frac{8+6}{2}$
X = 7

X = $\frac{8 -6}{2}$
X = 1

S{7,1}.