[SPLIT] solve 2v+18=16-4(v+7), 4x-(9-3x)=8x-1

Corey Franklin

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2v+18=16-4(v+7)
2v+18=16-4v-28
18=16+6v-28
2=6v-10
0=6v-12
0=v-6
???

4x-(9-3x)=8x-1
4x-12x=8x-1
8x=8x-1
x=-1
 

tkhunny

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Corey Franklin said:
2v+18=16-4v-28
18=16+6v-28
Whoops. Subtracting 2v makes -6v (Negative)

4x-(9-3x)=8x-1
4x-12x=8x-1
Whoops. Left side should be 4x - 9 + 3x. Where did you get 12x? 9+3? Don't do that.

Give them another go.
 

Corey Franklin

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Well, I think I did better on one of them; still confused on the other...

2v+18=16-4(v+7)
2v+18=16-4v-28
18=16-2v-28
2=2v-12
2v-10
v=-5

I know I shouldn't have added the 9 and the 3, guess I was too tired...
4x-(9-3x)=8x-1
4x-9+3x=8x-1
7x-9=8x-1
-9=1x-1
-8=1x
x=-8
 

Mrspi

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Dec 17, 2005
Messages
2,128
Corey Franklin said:
Well, I think I did better on one of them; still confused on the other...

2v+18=16-4(v+7)
2v+18=16-4v-28 you are correct up to this point.
Now, simplify the right-hand side by combining like terms:
2v + 18 = -4v - 12
Eliminate the variable term from one side.....it LOOKS like you have attempted to eliminate the 2v from the left side, which is ok. BUT, you'd need to add -2v to both sides to do that:
2v + 18 + (-2v) = -4v - 12 + (-2v)
18 = -6v - 12
Now, get the variable term by itself. To eliminate the " - 12" from the right side, ADD 12 to both sides:
18 + 12 = -6v - 12 + 12
30 = -6v
Divide both sides by -6:
30 / (-6) = (-6v) / (-6)
-5 = v

CHECK YOUR ANSWER. Is the original equation true when we substitute -5 for v?
2(-5) + 18 = 16 - 4(-5 + 7)
-10 + 18 = 16 - 4(2)
8 = 8 True. It checks.


18=16-2v-28 This step is incorrect and so is everything that follows this step.
2=2v-12
2v-10
v=-5 this is the correct answer, but IT DOES NOT COME from the work you've shown! (maybe it came from the back of the book??).

I know I shouldn't have added the 9 and the 3, guess I was too tired...
4x-(9-3x)=8x-1
4x-9+3x=8x-1
7x-9=8x-1
-9=1x-1
-8=1x
x=-8
 

tkhunny

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Did you check your answers?
 
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