Question

Dada a função f(x)= -2x+7, determine o valor de x em cada caso:
a) F(x)= 12
b) f(x)= -5
c) f(x)= -1/2

Answer 1

f(x)= -2x+7

a)

-2x+7 = 12

x= - 5/2 = -2,5

b)-2x+7=-5

x = 6

c) -2x+7 =-1/2

x=3,75

Espero ter ajudado

Abraços!

Answer 2

É dada a função $\mathsf{f(x)=-2x+7.}$ Vamos determinar o que se pede.

$\mathsf{a)\;f(x)=12}$

Para que $\mathsf{f(x)=12,}$ deve-se ter:

$\mathsf{-2x+7=12}\implies\\\\\implies\mathsf{-2x=12-7}\implies\\\\\implies\mathsf{-2x=5}\implies\\\\\implies\boxed{\mathsf{x=-\dfrac{5}{2}}}$

$\mathsf{b)\;f(x)=-5}$

Devemos ter:

$\mathsf{-2x+7=-5}\implies\\\\\implies\mathsf{-2x=-5-7}\implies\\\\\implies\mathsf{-2x=-12}\implies\\\\\implies\mathsf{x=\dfrac{-12}{-2}}\implies\\\\\implies\boxed{\mathsf{x=6}}$

$\mathsf{b)\;f(x)=-\dfrac{1}{2}}$

De maneira análoga, deve-se ter:

$\mathsf{-2x+7=-\dfrac{1}{2}}\implies\\\\\implies\mathsf{-2x=-\dfrac{1}{2}-7}\implies\\\\\implies\mathsf{-2x=-\dfrac{1}{2}-\dfrac{14}{2}}\implies\\\\\implies\mathsf{-2x=\dfrac{-15}{2}}\implies\\\\\implies\mathsf{x=\dfrac{\frac{-15}{2}}{-2}}\implies\\\\\implies\mathsf{x=\dfrac{-15}{2}\cdot\dfrac{1}{-2}}\implies\\\\\implies\boxed{\mathsf{x=\dfrac{15}{4}}}$

Dúvidas? Comente.