Multiply each term of $ \left( \color{blue}{x-1}\right) $ by each term in $ \left( x-2\right) $.

$$ \left( \color{blue}{x-1}\right) \cdot \left( x-2\right) = x^2-2x-x+2 $$

Combine like terms:

$$ x^2 \color{blue}{-2x} \color{blue}{-x} +2 = x^2 \color{blue}{-3x} +2 $$

Multiply each term of $ \left( \color{blue}{x^2-3x+2}\right) $ by each term in $ \left( x-3\right) $.

$$ \left( \color{blue}{x^2-3x+2}\right) \cdot \left( x-3\right) = x^3-3x^2-3x^2+9x+2x-6 $$

Combine like terms:

$$ x^3 \color{blue}{-3x^2} \color{blue}{-3x^2} + \color{red}{9x} + \color{red}{2x} -6 = x^3 \color{blue}{-6x^2} + \color{red}{11x} -6 $$

Multiply each term of $ \left( \color{blue}{x^3-6x^2+11x-6}\right) $ by each term in $ \left( x-4\right) $.

$$ \left( \color{blue}{x^3-6x^2+11x-6}\right) \cdot \left( x-4\right) = x^4-4x^3-6x^3+24x^2+11x^2-44x-6x+24 $$

Combine like terms:

$$ x^4 \color{blue}{-4x^3} \color{blue}{-6x^3} + \color{red}{24x^2} + \color{red}{11x^2} \color{green}{-44x} \color{green}{-6x} +24 = x^4 \color{blue}{-10x^3} + \color{red}{35x^2} \color{green}{-50x} +24 $$