salut
Aire AMQ= (b*h)/2
= (x(5-x))/2 => (5x-x²)/2
Aire BMN= (b*h)/2
= ((7-x)x)/2 => (7x-x²)/2
aire ABCD= 35
aire MNPQ= Aire ABCD - 2*Aire AMQ - 2*Aire BMN
= 35 - 2*((5x-x²)/2)-2*((7x-x²)/2)
= 35-5x+x²-7x+x²
Aire MNPQ = 2x²-12x+35
Aire MNPQ = 17cm²
2x²-12x+35=17
2x²-12x+18=0
delta=0 une solution -b/2a = 12/4=3
Aire MNPQ = 17 cm² pour x=3