(9) \( \left(4 x^{2}-8 x\right)-\left(7 x^{2}-x\right) \)

To simplify the expression, start by distributing the negative sign across the second parenthesis: \( (4x^2 - 8x) - (7x^2 - x) = 4x^2 - 8x - 7x^2 + x \). Now, combine like terms: First, for the \( x^2 \) terms: \( 4x^2 - 7x^2 = -3x^2 \). Next, for the \( x \) terms: \( -8x + x = -7x \). Putting it all together, you get: \( -3x^2 - 7x \). So, the simplified expression is: \( -3x^2 - 7x \).