X+y
мне кажется что так, ибо х это рабочий, вместе +, ученик у
1
2)3x-20y =11
<span>x+6y=10
3(10-6у)-20у=11
х=10-6у
30-18у-20у=11
38у=30-11
38у=19
у=19/38=1/2
х=10-6*1/2=10-3=7
3)</span>9x+3y= -6
<span>-1,5x+y=-5
</span><span>
9х+3(</span>1,5х-5)=-6<span>
у=1,5х-5
</span>
9х+3(1,5х-5)=-6
9х+4,5х-15=-6
13,5х=-6+15
13,5х=9
х=9/13,5=9*2/27=2/3
у=3/2*2/3-5=1-5=-4
![(1-b^2)*( \frac{1}{(b-1)^2} - \frac{1}{1-b^2})+ \frac{2b}{1+b} = (1-b^2)*( \frac{1+b-1+b}{(1-b)^2(1+b)}+ \frac{2b}{1+b}](https://tex.z-dn.net/?f=%281-b%5E2%29%2A%28+%5Cfrac%7B1%7D%7B%28b-1%29%5E2%7D+-++%5Cfrac%7B1%7D%7B1-b%5E2%7D%29%2B+%5Cfrac%7B2b%7D%7B1%2Bb%7D++%3D+%281-b%5E2%29%2A%28+%5Cfrac%7B1%2Bb-1%2Bb%7D%7B%281-b%29%5E2%281%2Bb%29%7D%2B+%5Cfrac%7B2b%7D%7B1%2Bb%7D)
=
=
![\frac{2b(1-b^2)}{(1-b^2)(1-b)} + \frac{2b}{1+b} = \frac{2b}{1-b} + \frac{2b}{1+b} = \frac{2b+2b^2+2b-2b^2}{1-b^2}= \frac{4b}{1-b^2}](https://tex.z-dn.net/?f=+%5Cfrac%7B2b%281-b%5E2%29%7D%7B%281-b%5E2%29%281-b%29%7D++%2B++%5Cfrac%7B2b%7D%7B1%2Bb%7D++%3D++%5Cfrac%7B2b%7D%7B1-b%7D+%2B++%5Cfrac%7B2b%7D%7B1%2Bb%7D+%3D++%5Cfrac%7B2b%2B2b%5E2%2B2b-2b%5E2%7D%7B1-b%5E2%7D%3D++%5Cfrac%7B4b%7D%7B1-b%5E2%7D++)
при подстановке получится
![- \frac{5}{6}](https://tex.z-dn.net/?f=-+%5Cfrac%7B5%7D%7B6%7D+)