Question

Punctul c)
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Answer 1

$x\circ x\circ x\stackrel{b)}{=} [(x+7)^2-7]\circ x=[(x+7)^2-7+7](x+7)-7=\\(x+7)^3-7\\Ecuatia~ devine:\\(x+7)^3-7=x\\(x+7)^3-x-7=0\\(x+7)^3-(x+7)=0\\(x+7)[(x+7)^2-1]=0\\Distingem~ doua~ cazuri:\\1.x+7=0\Rightarrow x=-7\\2.(x+7)^2-1=0\\  (x+7)^2=1|\sqrt{}\\|x+7|=1\\i)x+7=1\Rightarrow x=-6\\ii)x+7=-1\Rightarrow x=-8\\S:x\in \{-6,-7,-8\}$