Verified answer

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Умножим обе части на 12

[tex]\frac{(x+1)^{2} }{6} *\frac{12}{1} +\frac{(x-1)^{2} }{12} *\frac{12}{1} -\frac{x^{2} -1}{4}*\frac{12}{1} =1*12[/tex]

[tex]2(x+1)^{2} +1*(x-1)^{2} -3(x^{2} -1)=12[/tex]

2(x²+2x+1)+(x²-2x+1)-3x²+3=12

2x²+4x+2+x²-2x+1-3x²+3=12

2x+6=12

2x=6

x=3