Salut !!
Le triangle ECF est rectangle en C donc EC² + FC² = EF²
(6.3)² + (1.6)² = EF²
EF² = 39.69 + 2.56 = 42.25
EF = √42.25 = 6.5m
30cm = 0.3m
(EC - 0.3)² + (FC + x)² = EF²
6² + (1.6 + x)² = (6.5)²
36 + 2.56 + 3.2x + x² = 42.25
x² + 3.2x - 3.69 = 0
Δ = 10.24 - 4 × 1 × (-3.69) = 25
√Δ = 5
x₁ = (-3.2 - 5)/2 = -8.2 inacceptable
x₂ = (-3.2 + 5)/2 = 1.8
Donc il faut reculer le pied 1.8m en arrière.
