a²-a=a(a-1)
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a) 4x(2x-1)-(x-3)(x+3)=(8x-4)*x-(x-3)*(x+3)=8x^2-4x-(x-3)*(x+3)=8x^2-4x-(x^2-9)=8x^2-4x-x^2+9=7x^2-4x+9