bonjour
côté initial = x donc aire initiale = x²
( x + 5 )² = 4 x²
x² + 10 x + 25 = 4 x²
x² - 4 x² + 10 x + 25 = 0
- 3 x² + 10 x + 25 = 0
Δ = 100 - 4 ( - 3 * 25) = 100 + 300 = 400 = 20²
x 1 = ( - 10 - 20 ) / - 6 = - 30 /-6 = 5
x 2 = ( - 10 + 20 ) / - 6 = - 10 /6 non retenue
x = 5 cm
aire initiale = 25 cm²
nouvelle aire = 10 ² = 100
4 x 25 = 100
