Question

помогите пожалуйста ​

Answer 1

$\displaystyle\bf\\\frac{s-f}{f^{2} +s^{2} } \cdot\Big(\frac{f+s}{f} -\frac{2f}{f-s} \Big)=\frac{s-f}{f^{2} +s^{2} } \cdot\frac{(f+s)\cdot(f-s)-2f\cdot f}{f(f-s)} =\\\\\\=\frac{s-f}{f^{2}+s^{2} } \cdot\frac{f^{2}-s^{2} -2f^{2} }{f(f-s)}=\frac{s-f}{f^{2}+s^{2} }\cdot\frac{f^{2} +s^{2} }{f(s-f)} =\frac{1}{f}\\\\\\f=2 \ \ \Rightarrow \ \ \frac{1}{f} =\frac{1}{2} =0,5\\\\Otvet:0,5$