Question

Dizer para que valores reais de x as expressões a seguir assumem valores nulos, positivos ou negativos.





a) – 4x² + 7x

b) 9x² - 42x + 49

c) x² - 2x + 3

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Answer 1

Boa Tarde !!!

a) a = -4/b = 7/ c = 0/

Δ = $b^{2} -4.a.c$

Δ = 49 - 4.(-4).0

Δ = 49

$\frac{-b-+\sqrt{49} }{2.a}$

$\frac{-7-+7}{2}$

x1 = -14/2

x1 = -7

x2 = 0/2

x2 = 0

s = {0, -3}

b) a = 9/b = -42/ + 49/3

Δ = b² -4.a.c

Δ = 1764 - 4.9.49

Δ = 1764 - 1764

Δ = 0

$\frac{-b-+\sqrt{0} }{2.a}$

$\frac{42-+0}{18}$

x1 = 42/18

x1 = 2, 333...

x2 = 42/18

x2 = 2,333...

s = {2,333...}

c) a = 1/ b = -2/ x = 3

Δ = b²-4.a.c

Δ = 4 - 4.1.3

Δ = 4 - 12

Δ = -8

Δ = ∉

Espero ter ajudado :-)

Att: LDC