[tex]4\cdot (3+x)^{2} -(2x-1)\cdot (2x+1) \leq 13\\
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4\cdot (9+6x+x^{2} )-(4x^{2} -1) \leq 13 \\
korzystam~~ze~~wzorow~~skroconego~~mnozenia:\\
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(x+y)^{2} =x^{2} +2xy+y^{2} ~~oraz~~(x+y)\cdot (x-y)= x^{2} -y^{2} \\
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36+24x+4x^{2} -4x^{2} +1 \leq 13\\
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24x+36+1 \leq 13\\
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24x+37 \leq 13\\
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24x\leq 13-37\\
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24\leq -24~~\mid \div 24\\
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x \leq -1\\
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x\in ( - \infty ,-1>[/tex]
