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Rearrange the formula

  • Thread starter Gringo123
  • Start date
  • #1
141
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I need to rearrange this formula to make e the subject. Have I done it correctly?

10b + 5be - 3e + 7c
10b + 5be - 3e = 7c
5be - 3e = 7c - 10b
e(5b - 3) = 7c - 10b

e = 7c - 10b / 5b - 3
 

Answers and Replies

  • #2
33,505
5,191
I need to rearrange this formula to make e the subject. Have I done it correctly?
You're not starting with an equation! Without the first line below being an equation, you can't solve for anything.
10b + 5be - 3e + 7c
10b + 5be - 3e = 7c
5be - 3e = 7c - 10b
e(5b - 3) = 7c - 10b

e = 7c - 10b / 5b - 3
Assuming that this is your starting equation -- 10b + 5be - 3e = 7c -- your work following it is fine, EXCEPT that you need to use parentheses. You should write e this way:
e = (7c - 10b) / (5b - 3)
 
  • #3
141
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Thanks a lot Mark
 
  • #4
9
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You're not starting with an equation! Without the first line below being an equation, you can't solve for anything.

Assuming that this is your starting equation -- 10b + 5be - 3e = 7c -- your work following it is fine, EXCEPT that you need to use parentheses. You should write e this way:
e = (7c - 10b) / (5b - 3)
Well if we assume that the first line is an equation (set equal to zero): 10b + 5be - 3e + 7c=0, then the second line changes:

10b + 5be - 3e = -7c, and that would change the rest of the steps which follow...
 

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