Question

помогите пожалуйста!!
Решить уравнение: х!/(х-2)!=42
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Answer 1

$\displaystyle\bf\\\frac{x!}{(x-2)!} =42\\\\\\\frac{(x-2)!\cdot(x-1)\cdot x}{(x-2)!} =42\\\\\\(x-1)\cdot x=42\\\\x^{2} -x-42=0\\\\D=(-1)^{2}-4\cdot (-42)=1+168=169=13^{2} \\\\\\x_{1} =\frac{1+13}{2} =7\\\\\\x_{2} =\frac{1-13}{2} =-6 < 0-neyd\\\\\\Otvet \ : \ 7$