SOLUTION: I thought I was getting the hang of this but the more math I try to do I think I get more confused. I have done this three times and got three different answers.0,-9 and 9 The pr

Question 174163: I thought I was getting the hang of this but the more math I try to do I think I get more confused. I have done this three times and got three different answers.0,-9 and 9
The problem is --- Find the value of 5z-9 given that -9z-9=9 thanks in advance. Judy
Answer by gonzo(654) (Show Source): You can put this solution on YOUR website!
find the value of 5z-9 given that -9z-9 = 9
your second equation should give you the value of z.
let's see what happens:
-9z - 9 = 9
add 9 to both sides of the equation to get:
-9z -9 + 9 = 9 + 9
combining like terms we get:
-9z = 18
divide both sides by 9 and we get:
-9z/9 = 18/9
simplifying, we get:
-z = 2
multiplying both sides by -1 we get:
-z*-1 = 2*-1
simplifying we get:
z = -2
-----
to see if this value of -2 is correct, we substitute -2 for z in the equation:
-9z-9=9
this becomes:
-9*(-2) - 9 = 9
which becomes:
18 - 9 = 9
which becomes:
9 = 9
so we know the value of z = -2 is good.
-----
since z = -2, none of your answers should be good.
let's go through anyway.
let z = 0:
-9z-9 = 9
-0-9 = 9
-9 = 9 is not true so this answer is no good.
-----
let z = 9
-9z-9 = 9
-9*9-9 = 9
-81-9 = 9
not true again, so this answer is no good.
-----
let z = -9
-9z-9 = 9
-9*-9 - 9 = 9
81-9 = 9
again not true.
-----
z = -2
let y = 5z-9
if z = -2, then
y = 5*(-2) - 9
removing parentheses:
y = -10 - 9
combining like terms:
y = -19
-----
your answer is:
if -9z-9 = 9, then z = -2, and 5z-9 = -19
-----
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