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$\Longrightarrow (9c_1 e^{3x}+3c_{2}e^{3x}+9c_2 xe^{3x}+3c_2 e^{3x})-18c_1 e^{3x}-6c_2 e^{3x}-18c_2 xe^{3x}+9c_1 e^{3x}+9c_{2}xe^{3x}=0$\\
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