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Bonjour,
1)aire de la plaque initiale=x^2
aire du H =2x*60+30*(x-120)=120x+30x-3600=150x-3600
==>aire restante
A(x)=x^2-150x+3600=(x-75)^2-75^2+3600=(x-75)^2-2025
2)1000≤(A(x) ≤ 2200
1000≤ (x-75)^2-2025≤ 2200
3025≤(x-75)^2≤4225
x≥120
x-75≥120-75≥0
√3025≤x-75≤√4225
55≤x-75≤65
55+75≤x≤65 + 75
130 ≤ x ≤ 140
1)aire de la plaque initiale=x^2
aire du H =2x*60+30*(x-120)=120x+30x-3600=150x-3600
==>aire restante
A(x)=x^2-150x+3600=(x-75)^2-75^2+3600=(x-75)^2-2025
2)1000≤(A(x) ≤ 2200
1000≤ (x-75)^2-2025≤ 2200
3025≤(x-75)^2≤4225
x≥120
x-75≥120-75≥0
√3025≤x-75≤√4225
55≤x-75≤65
55+75≤x≤65 + 75
130 ≤ x ≤ 140