A=81x²-72xy+16y²  (1)
A = (9x)² - 72xy + (4y)²
A = (9x - 4y)²
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B= ((9/64)x² + (3/4)x + 1  
B= ((3/8)x)² + (3/4)x + 1  
B = ((3/8)x + 1)²
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C = (9/16)x² + (5/2)x + 25/9
C = ((3/4)x)² + (5/2)x + (5/3)²
C = ((3/4)x + (5/3))²
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D = (49/9)x² - (4/121)
D = ((7/3)x)² - (2/11)²
D = ((7/3)x - (2/11))((7/3)x + (2/11))
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E = (16/9) - (2x-5)²
E = (4/3)² - (2x-5)²  
E = ((4/3) - (2x-5))((4/3) + (2x-5))
E = ((4/3)+5 - 2x)((4/3)-5 + 2x)
E = ((19/3) - 2x)(2x - (11/3))
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F = (3-2x)²-(-3+5x²)
Verifie l'énoncé , je renifle une erreur.
A supposer qu'il n'y ait pas d'erreur, alors:
F = 9 - 12x + 4x² + 3 - 5x²
F = -x² - 12x + 12
x = [6 +/- V(36 + 12)]/(-1)
x = -6 +/- V(48)
x = -6 +/- 4V3
F = -(x +6 + 4V3)(x +6 - 4V3)
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G = 4x-5-(7+x)(4x-5)
G = (4x-5).(1-(7+x))
G = -(4x-5).(x+6)
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Sauf distraction.