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f(x) = 2x²-16x+60
f(x) = 30 ====> 2x²- 16x+60 = 30 ===> 2x²-16x+30 = 0
2(x-5)(x-3) = 0 ===> 2(x²-8x+15) = 0 ==> 2x²-16x+30 = 0
conclusion f(x) = 0 si un des facteurs est nul
f(x) = 0 si x-5 = 0 pour x = 5
ou x-3 = 0 pour x = 3
f(x) = 2x²-16x+60
f(x) = 30 ====> 2x²- 16x+60 = 30 ===> 2x²-16x+30 = 0
2(x-5)(x-3) = 0 ===> 2(x²-8x+15) = 0 ==> 2x²-16x+30 = 0
conclusion f(x) = 0 si un des facteurs est nul
f(x) = 0 si x-5 = 0 pour x = 5
ou x-3 = 0 pour x = 3