[latex] \frac{1}{4x} - \frac{4x+5y}{20xy} [/latex] при [latex]x= \sqrt{21} [/latex], [latex]y= \frac{1}{4} [/latex]

[latex] \frac{5y}{20x*y} - \frac{4x+5y}{20xy} = \frac{5y-4x-5y}{20xy} =- \frac{4x}{20xy} = -\frac{1}{5y} [/latex]=[latex]- \frac{4}{5} [/latex]