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How do I reverse this equation?

I have the following equation but would like to isolate L:

P = 5L^2 + 5L

How do I get L as a function of P?

Note that the "^" symbol represents an exponent.

Update:

If it can in any way simplify the answer, note that both L and P are always positive values.

2 Answers

Relevance
  • 1 decade ago
    Favorite Answer

    P = 5L² + 5L

    Try quadratic?

    5L² + 5L - P = 0

    L = (-5 ± √(25 + 20P))/10

    Another approach: complete the square:

    P/5 = L² + L

    (P/5) + 1/4 = L² + L + 1/4

    (P/5) + 1/4 = (L + 1/2)²

    L + 1/2 = √((P/5) + 1/4)

    L = √((P/5 + 1/4) - 1/2

  • 1 decade ago

    Complete the square then you can solve the equation for L:

    P = 5L² + 5L

    P = 5(L² + L)

    4P = 5(4L² + 4L)

    4P = 5[(2L + 1)² - 1]

    (2L + 1)² - 1 = 4P / 5

    (2L + 1)² = 4P / 5 + 1

    2L + 1 = √(4P / 5 + 1)

    2L = √(4P / 5 + 1) - 1

    L = [√(4P / 5 + 1) - 1] / 2

    L = [√{(4P + 5) / 5} - 1] / 2

    L = [√(4P + 5) / √5 - 1] / 2

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