Question

Determine os zeros ou raízes das funções: Marque a correta em cada função a) f(x) = x2 – 4x – 5
(a ) 2 e 5. (b) -1 e 5. (C) -2 e – 4. (d) 3 e 5.
b) f(x) = x2 – 4x + 4
(a) 3 (b) 0 (c) 2 (d)∅

c) f(x) = x2 – 2x + 6
(a) -3. (b) 1. (c) 2. ( d) ∅.

Answer 1

Explicação passo-a-passo:

1) $\sf f(x)=x^2-4x-5$

$\sf x^2-4x-5=0$

$\sf \Delta=(-4)^2-4\cdot1\cdot(-5)$

$\sf \Delta=16+20$

$\sf \Delta=36$

$\sf x=\dfrac{-(-4)\pm\sqrt{36}}{2\cdot1}=\dfrac{4\pm6}{2}$

$\sf x'=\dfrac{4+6}{2}~\longrightarrow~x'=\dfrac{10}{2}~\longrightarrow~x'=5$

$\sf x"=\dfrac{4-6}{2}~\longrightarrow~x"=\dfrac{-2}{2}~\longrightarrow~x"=-1$

Letra B

2) $\sf f(x)=x^2-4x+4$

$\sf x^2-4x+4=0$

$\sf (x-2)^2=0$

$\sf x-2=0$

$\sf x'=x"=2$

Letra C

3) $\sf f(x)=x^2-2x+6$

$\sf x^2-4x-5=0$

$\sf \Delta=(-2)^2-4\cdot1\cdot6$

$\sf \Delta=4-24$

$\sf \Delta=-20$

Não tá raízes reais

Letra D