Question

$frac{1}{4x} - frac{4x+5y}{20xy}$ при $x= sqrt{21}$, $y= frac{1}{4}$

Answer 1

$frac{5y}{20x*y} - frac{4x+5y}{20xy} = frac{5y-4x-5y}{20xy} =- frac{4x}{20xy} = -frac{1}{5y}$=$- frac{4}{5}$