help with an easy math problem making 'r' the subject?

r^2+r=A/2ph ....make r the subject

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  • 6 years ago
    Favorite Answer

    r^2+r=A/(2ph)?

    If so, then

    r^2+r-A/(2ph)=0=>

    r=[-1+/-sqrt(1+2A/(ph)]/2

    =>

    r=[-1+sqrt(1+2A/(ph))]/2

    or

    r=[-1-sqrt(1+2A/(ph))]/2

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  • Ron W
    Lv 7
    6 years ago

    Complete the square on r:

    r² + r + (1/2)² = A/(2ph) + (1/2)²

    (r + (1/2))² = A/(2ph) + 1/4

    r + (1/2) = ±√(A/(2ph) + 1/4)

    r = -(1/2) ± √(A/(2ph) + 1/4)

    This is precisely what you'd get if you wrote the equation as

    r² + r - (A/(2ph)) = 0

    and then applied the quadratic formula.

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