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Solving equations :/

  1. Nov 22, 2011 #1
    1. The problem statement, all variables and given/known data

    Solve each of the following equations. This is part of a practice mock test I have for an exam so I have all the answers but they aren't lining up somewhere. I got a) right but b) and c) wrong

    2. Relevant equations

    a)4x+6=18
    b)5x+7=7x-9
    c)1/x+2 = 7 (giving answer rounded to 4 decimal places)

    3. The attempt at a solution
    The first was easy, the rest though :/
    a:
    4x+6=18
    4x=12
    x=3

    b:
    5x+7 = 7x-9
    -2X = -2
    X= 4


    c:
    1/x+2 = 7
    x+2 = (7*1)
    x=5

    the answer they got was -1.8571...

    Please help guys this basic stuff is killing me! I can do that advanced stuff no problem (this is for a degree in Engineering) but this basic stuff is a nightmare!!
     
  2. jcsd
  3. Nov 22, 2011 #2

    Mark44

    Staff: Mentor

    You should write this as 1/(x + 2) = 7. Without the parentheses, 1/x + 2 means (1/x) + 2, which is not what you intend.
    Divide both sides of the equation -2x = -2 by -2. The solution is not x = 4.
    Again, write the equation as 1/(x + 2) = 7. Now, if two numbers are equal, their reciprocals are equal, so the next equation is
    x + 2 = 1/7
    Can you finish this?
     
  4. Nov 22, 2011 #3

    eumyang

    User Avatar
    Homework Helper

     
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