Question

07. Resolva a equação x2 – 3x – 18 = 0 no caderno e assinale as opções que represe
x'ex?
a) x1 = 2 e x2 = 4
b) x1 = 6 e x2 = -3
c) x1 = 6 e x2 = 3​

Answer 1

Resposta:

1)4x-1=7

4x=7+1

x=8/4

x=2

2)3x-9=12

3x=12+9

x=21/3

x=7

5)2x-6=16

2x=16+6

x=22/2

x=11

7)4x-7=2x-8

4x-2x=-8+7

2x=-1

x=-1/2

8)6x-3=12-9x

6x+9x=12+3

15x=15

x=1

9)x+4-3x=4-12x

x-3x+12x=4-4

10x=0

x=0

10)6x-4+12=3+4x-9

6x-4x=-4+12-3+9

2x=14

x=14/2

x=7

13)3(x+2)=15

3x+6=15

3x=15-6

x=9/3

x=3

15)12x+3(x-1)=-2(x-1)+12

12x+3x-3=-2x+2+12

12x+3x+2x=2+12+3

17x=17

x=17/17

x=1

16)2(x-1)=0

2x-2=0

2x=0-2

x=-2/2

x=1

17)3(x+2)=15

3x+6=15

3x=15-6

x=9/3

x=3

18)2(x+2)=12

2x+4=12

2x=12-4

x=8/2

x=4

22)5(x-4)=1+9(x-1)

5x-20=1+9x-9

5x-9x=1-9+20

-4x=28

x=28/-4

x=-7

Explicação passo-a-passo:

(3,4,6,11,12,14,19,20,21,23,24,25,26,30

Answer 2

Resposta:

$\sf x^2 -3x - 18 = 0$

$\sf \Delta = b^2 -\:4ac$

$\sf \Delta = (-\: 3)^2 -\:4 \cdot 1 \cdot (-\:18)$

$\sf \Delta = 9 + 72$

$\sf \Delta = 81$

$\sf x = \dfrac{-\,b \pm \sqrt{\Delta} }{2a} = \dfrac{-\,(-\:3) \pm \sqrt{81} }{2\cdot 1} = \dfrac{3 \pm 9 }{2} \Longrightarrow\begin{cases} \sf x_1 = &\sf \dfrac{3 + 9}{2} = \dfrac{12}{2} = \;6 \\\\ \sf x_2 = &\sf \dfrac{ 3 -\: 9 }{2} = \dfrac{- \; 6}{2} = - \: 3\end{cases}$

$\sf \boldsymbol{ \sf \displaystyle S = \{ x \in \mathbb{R} \mid x = 6 \mbox{\sf \;e } x = -\: 3 \} }$

Alternativa correta é a letra B.

Explicação passo-a-passo: