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How Do You Use the Solution from an Equation to Evaluate an Expression?

If 3x=21, what is 9x?

Summary

  1. 'x' is a variable
  2. Dividing by '3' will cancel out the multiplication by '3' on the left side of the equation
  3. 21/3 = 7
  4. For '9x', we plugged our answer '7' in for 'x' to get '9(7)', or '63'

Notes

    1. 'x' is a variable
    1. 'x' is a variable
    1. Dividing by '3' will cancel out the multiplication by '3' on the left side of the equation and give us 'x' by itself
    2. 'x' is a variable
    1. Dividing by '3' will cancel out the multiplication by '3' on the left side of the equation and give us 'x' by itself
    2. 'x' is a variable
    1. 21/3 = 7
    1. Since we got 'x' by itself on the left side, 'x = 7'
    2. 'x' is a variable
    1. For '9x', we plug our answer '7' in for 'x'
    2. 'x' is a variable
    1. For '9x', we plug our answer '7' in for 'x' to get '9(7)', or '63'
    2. 'x' is a variable
    1. So when 'x' is '7', '9x' becomes '63'
    2. 'x' is a variable
    1. 'x' is a variable