Question

По фотке помогите математика. 10 класс

Answer 1

$\displaystyle\bf\\f(x)=\frac{3}{5-4x} \\\\\\f'(x)=\frac{3'\cdot(5-4x)-3\cdot(5-4x)'}{(5-4x)^{2} } =\frac{0\cdot(5-4x)-3\cdot(-4)}{(5-4x)^{2} } =\\\\\\=\frac{12}{(5-4x)^{2} } \\\\\\f'(0,5)=\frac{12}{(5-4\cdot0,5)^{2} } =\frac{12}{(5-2)^{2} } =\frac{12}{3^{2} } =\frac{12}{9} =\frac{4}{3} \\\\\\Otvet:\frac{4}{3}$