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What's the Direct Variation or Direct Proportionality Formula?

Definition: Direct Variation

Summary

  1. In direct variation, as one value increases so does the other
  2. 'x' and 'y' are variables
  3. 'k' is the constant of variation
  4. 'k' cannot equal 0
  5. 'y' represents the circumference, which is unknown
  6. 'x' represents the length of a side, which is 5
  7. 'k', the constant, is 4
  8. The circumference of the square is 20

Notes

    1. In direct variation, as one value increases so does the other
    1. In direct variation, as one value increases so does the other
    2. 'x' and 'y' are variables
    3. 'k' is a constant
    4. As 'x' increases, 'y' also increases
    1. Since 'k' is a constant, it stays the same for any 'x' and 'y'
    1. If we know 'k' and either 'x' or 'y', we can use our formula to find the unknown variable
    1. Since we're multiplying 'x' by a constant, 'y' will increase when 'x' does
    1. These two phrases mean the same thing
    2. You may also hear the phrase 'varies directly'
    3. That means 'direct variation' as well
    1. We need to figure out what 'y', 'x', and 'k' are in our problem
    1. 'Directly proportional' means we will use the formula for direct variation
    2. The circumference and the length are directly proportional to each other
    1. One of our variables, 'y', will represent the circumference
    1. The circumference, 'y', is our unknown
    1. Our other variable, 'x', will represent the length of a side
    1. The problem gives us a value for the length of a side, 5
    2. So x=5
    1. The constant of variation is given, so k=4
    1. Our formula was y=k•x
    2. So y=4•5