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Rearrange the formula to make r the subject

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    A=4+r(squared)
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    A-4=r^2
    (root)A-4=r
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    (Original post by questioner...)
    A=4+r(squared)
    A=4+ r2

    Subtract 4 from both sidesA - 4 = r2

    Square root both sides
    √ (A-4) = r (Make sure the square root extends over the whole of A-4)

    r= √(A-4)
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    (Original post by natalijka09)
    A=4+r(squared)
    A-4= r(squared)
    (root)(A-4)= r
    (root)A - 2= r
    No full answers please. Especially none where you don't know how roots work.
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    If you do an operation on one side of an equation, that equation can only hold if the same operation occurs on the other. You need to 1. get an equation in terms of everything not r on one side, and everything r on the other, 2. reduce the equation to r= (something without r).
 
 
 
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