f(x)=(2-5x)-8+20x      

factoriser:
f(x)=(2-5x)-4(2-5x)
f(x) =-3.(2-5x)        

développer:
f(x) = 15x - 6

f(0) = -6
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g(x)=4*(x-1)²-9x²
factoriser:
g(x) = (2(x-1) - 3x)(2(x-1) + 3x)
g(x) = (-x-2)(5x-2)
g(x)= -(x+2)(5x-2)

développer:
g(x) = 4(x²-2x+1) - 9x²
g(x) = -5x²-8x+4
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g(-3) = -5*9 + 24 + 4 = -17

g(1+V2) = 4*(V2)² - 9.(1+V2)²
g(1+V2) = 4*2 - 9.(1+2V2+2)
g(1+V2) = 8 - 9.(3+2V2)
g(1+V2) = -19 - 18V2
-----------
g(x) = -5x²-8x+4 = 0
-(x+2)(5x-2)=0
x = -2 et x = 2/5
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g(x) = -4x
-5x²-8x+4 = -4x
5x²+4x-4 = 0

x = [-2 +/- V(4 + 20)]/5
x = [-2 +/- V(24)]/5
x = [-2 +/- 2V(6)]/5
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g(x) = f(x)
-5x²-8x+4 = 15x - 6
5x² + 23x - 10 = 0
x = [-23 +/- V(23² + 200)]/10
x = [-23 +/- 27]/10
x = 2/5 et x = -5
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Sauf distraction, refais les calculs.