width x
lenght : x + 11
area = x * (x+11) = 60 cm²
x² + 11x - 60 = 0
Δ = 11² - 4*1*(-60) = 121 + 240 = 361 = 19²
x' = (-11 - 19) / 2 = not possible
x" = (-11 + 19) / 2 = 4
witdh = 4
lenght = 4+11 = 15
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