Question 668176
Starting with
{{{(2r-5)^2 = 81}}}
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(2r-5)(2r-5) = 81
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{{{4r^2 - 10r - 10r + 25 = 81}}}
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{{{4r^2 - 20r - 56 = 0}}}
(4r+8)(r-7) = 0
4r+8 = 0, so r = {{{highlight_green(-8/4 = -2)}}}
r-7 = 0, so r = {{{highlight_green(7)}}}
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Solutions
-2 and 7
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