Salut!
a) C' A² = 8² + 12² = 64 + 144 = 208
B'A² = 8² + 4² = 64 + 4²
B'C¹² = 8² + ( 12 - x )²
64 + 4² = 208 + 8² + ( 12 - x )²
x² = 208 + x² - 24x + 144
24x = 352
x = 352 : 24
x = 44 / 3
b) B'C'² = 8² + ( 12 - x ) ²
B' A ² = 64 + n - 2
64 + n² = 8² + ( 12 - x ) ²
x² = x² - 24x + 144
24x = 144
x = 144 : 24
x = 12 cm
Succes!