\(P=\left(x+3\right)^2+\left(x-3\right)\left(x+3\right)-2\left(x+2\right)\left(x-4\right)=x^2+6x+9+x^2-9-2x^2+4x+16=10x+16=10.\left(-\dfrac{1}{2}\right)+16=11\)
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