Наиболее рациональным способом найти числовое значение дроби при x = 2; y=-1/3; z=-1/5 :[latex] \frac{\frac{7}{60}x - \frac{1}{4}y+ \frac{1}{18}z}{\frac{1}{5}x + \frac{1}{3}y+ \frac{7}{12}z} [/latex]

[latex]\frac{\frac{7}{60}x-\frac{1}{4}y+\frac{1}{18}z}{\frac{1}{5}x+\frac{1}{3}y+\frac{7}{12}z}= \frac{\frac{7}{60}x*180-\frac{1}{4}y*180+\frac{1}{18}z*180}{\frac{1}{5}x*180+\frac{1}{3}y*180+\frac{7}{12}z*180}=\frac{21x-45y+10z}{36x+60y+105z}\\ x=2;\ y=-\frac{1}{3};\ z=-\frac{1}{5}\\ \frac{21*2-45*(-\frac{1}{3})+10*(-\frac{1}{5})}{36*2+60*(-\frac{1}{3})+105*(-\frac{1}{5})}= \frac{42+15-2}{72-20-21}=\frac{55}{31}[/latex]