Question

Dada a função f: R-R definida por f(x) = -2x -6, calcule:
a) f (-3)
b) f (0)
c) f (x) = - 25
d) f (x) = 0
e) f (-1/3)
f) f (x) = 1/4

Answer 1

a) f (-3) = -2(-3) - 6 ==> 6-6= 0

b) f (0)= -2(0) - 6 ==> - 6

c) f (x) = - 25 => -2x - 6 = - 25 => -2x= -25+6=> -2x = - 19(-1)=>2x= 19

=>x= 19/2 

d) f (x) = 0 =>= -2x-6=0=> -2x = 6(-1)=>2x = - 6 ==> x = - 3
 
e) f (-1/3)= -2(-1/3) - 6

==> 2 - 6 ==> 2 - 18 ==> - 16
       3                3              3

f) f (x) = 1/4 ==> -2x - 6 = 1      mmc =4
                                      4

-8x - 24 = 1 ==> -2x = 1 + 24 ==> -2x = 25(-1) ==> 2x = - 25

x = - 25
         2

Answer 2

a.  f(-3)=- 2(-3) - 6 => f(-3) = 6 -6 = 0
b. f (0) = -2.0 - 6 = - 6  
c. f (x) = - 25  => -25 = -2x -6 => -19/-2=x => x = 19/2
d) f (x) = 0 => 0 = -2x -6 => -2x = 6 => x =6 / -2 => x =-3
e) f (-1/3) =-2x - 6 => f(-1/3)= -2(-1/3) - 6 => f(-1/3)= +2/3 - 6 =>  f(-1/3) = -16/3
f) f (x) = 1/4 => 1/4= - 2 x - 6 => 4(-2x - 6 ) = 1 => -8x =1 + 24=> x = - 25 / 8