$\text{a)}w\left(x\right)=9x^3-x=x\left(9x^2-1\right)=x\left(3x-1\right)\left(3x+1\right)$  

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$\text{b)}w\left(x\right)=50x^4-8x^2=2x^2\left(25x^2-4\right)=2x^2\left(5x-2\right)\left(5x+2\right)$  

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$\text{c)}w\left(x\right)=12x^3-27x^5=-3x^3\left(-4+9x^2\right)=-3x^3\left(9x^2-4\right)=-3x^3\left(3x-2\right)\left(3x+2\right)$