\[\boxed{\mathbf{23.}}\]
\[\mathrm{\Delta}f = f\left( x_{0} + \mathrm{\Delta}x \right) - f\left( x_{0} \right)\]
\[\textbf{а)}\ f(x) = - 2x + 1;x_{0} = 0;\ \]
\[\ \mathrm{\Delta}x = 0,1:\]
\[\mathrm{\Delta}f = f(0 + 0,1) - f(0) = f(0,1) -\]
\[- f(0) = 0,8 - 1 = - 0,2.\]
\[\textbf{б)}\ f(x) = - 2x + 1;x_{0} = 1;\ \]
\[\ \mathrm{\Delta}x = 0,1:\]
\[\mathrm{\Delta}f = f(1 + 0,1) - f(1) =\]
\[= f(1,1) - f(1) =\]
\[= - 1,2 + 1 = - 0,2.\]
\[\textbf{в)}\ f(x) = - 2x + 1;x_{0} = 1;\ \ \]
\[\mathrm{\Delta}x = - 0,1:\]
\[\mathrm{\Delta}f = f(1 - 0,1) - f(1) =\]
\[= f(0,9) - f(1) =\]
\[= - 0,8 + 1 = 0,2.\]
\[\textbf{г)}\ f(x) = - 2x + 1;x_{0} = - 1;\ \]
\[\ \mathrm{\Delta}x = 0,01:\]
\[\mathrm{\Delta}f = f( - 1 + 0,01) - f( - 1) =\]
\[= f( - 0,99) - f( - 1) =\]
\[= 2,98 - 3 = - 0,02.\]