Question 267551
A square has all its edge lenghts increased by 3cm.
This makes a new square with twice the area of the old one.
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Call the original side length s
The original area is s^2.
(s+3)*(s+3) = 2s^2
s^2 + 6s + 9 = 2s^2
s^2 - 6s - 9 = 0
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*[invoke solve_quadratic_equation 1,-6,-9]
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Ignore the negative answer
{{{s = 3 + 3sqrt(2)}}} cm
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It's probably messier than you expected.