Questions on Algebra: Absolute value answered by real tutors!

Algebra ->  Algebra -> Questions on Algebra: Absolute value answered by real tutors!     (Log On)
Ad: Algebra Solved!™: algebra software that solves YOUR algebra homework problems with step-by-step help!



Question 153627This question is from textbook McDougal Littell Algebra2
: Please help me solve this problem abs(f+3)=2f+4This question is from textbook McDougal Littell Algebra2
: Please help me solve this problem abs(f+3)=2f+4
Answer by Edwin McCravy(2087) About Me  (Show Source):
You can put this solution on YOUR website!
Please help me solve this problem abs(f+3)=2f+4

There are two cases to consider: 

Case 1:  abs(f+3)=2f+4 where f+3>=0

Case 2:  abs(f+3)=2f+4 where f+3<0

Let's do case 1 first:

abs(f+3)=2f+4 where f+3>=0

Then to get rid of the absolute value bars, we can just drop
them because the absolute value of any positive number
is just that positive number and the absolute value of 0
is also just that number, 0.  So

abs(f+3)=2f+4  becomes

f+3=2f+4

Solve that and get f=-1

So that is one solution, for when we check it,

abs(f+3)=2f+4
abs(-1+3)=2(-1)+4
abs(2)=-2+4
2=2


------

Now let's do case 2:

abs(f+3)=2f+4 where f+3<0

Here f+3 is a negative number. Therefore to get 
rid of the absolute value bars, we can make the negative 
number f+3 positive by multiplying it by -1.  So

abs(f+3)=2f+4  becomes

-1(f+3)=2f+4

Solve that and get f=-7/3

However that is not a solution, for when we check it,

abs(f+3)=2f+4
abs(-7/3+3)=2(-7/3)+4
abs(-7/3+9/3)=-14/3+4
abs(2/3)=-14/3+12/3
abs(2/3)=-2/3
2/3=-2/3

So there is just one solution, f=-1

Edwin