Question

найдите значение выражения 1/4х - 4х+5у/20ху при х=√21, у=1/4

Answer 1

$\frac{1}{4x} - \frac{4x+5y}{20xy} =\frac{1}{4x} - (\frac{4x}{20xy} +\frac{5y}{20xy})=\frac{1}{4x}-\frac{1}{5y}-\frac{1}{4x} =-\frac{1}{5y} = - \frac{1}{5 \frac{1}{4} } = \frac{4}{5}$