Urgen SVP!!! Mathématiques

bonjour,

on admet que ABC est rectangle en B

1) (MN)//(BC)
 →thales
AM/AB=AN/AC=NM/BC
AM/200 = x/150
AM = 200x/150 = 4x/3

2) A AMN = (NM*AM)/2
                 = [x(4x/3]/2
                 = (4x²/3)/2
                 = 4x²/6 = 2x²/3

A ABC = (150*200)/2  =15000m²
A BNCM = 150000-(2x²/3)

4) 15000-(2x²/3) = 2x²/3
-2x²/3-2x²/3 = -15000
-4x²/3 = -15000
4x² = 15000*3
4x² = 45000
x² = 11250
x = √11250 = 75√2(m)