M^3 = m-m
m*m*m = m-m
m = 0
![m^2+2mn+3m-2n-4 =\dfrac{1}{2}( 2m^2+4mn+6m-4n-8 )=\dfrac{1}{2}( m^2+4mn+4n^2+m^2+6m+9-9-4n^2-4n-1-7 )=\dfrac{1}{2}( (m+2n)^2+(m+3)^2-(2n+1)^2-4^2 )=\dfrac{1}{2}( (m+2n+2n+1)(m+2n-2n-1)+(m+3+4)(m+3-4) )=\dfrac{1}{2}( (m+4n+1)(m-1)+(m+7)(m-1) )=\dfrac{1}{2}(m+4n+1+m+7)(m-1)=(m+2n+4)(m-1)](https://tex.z-dn.net/?f=m%5E2%2B2mn%2B3m-2n-4%20%3D%5Cdfrac%7B1%7D%7B2%7D%28%202m%5E2%2B4mn%2B6m-4n-8%20%29%3D%5Cdfrac%7B1%7D%7B2%7D%28%20m%5E2%2B4mn%2B4n%5E2%2Bm%5E2%2B6m%2B9-9-4n%5E2-4n-1-7%20%29%3D%5Cdfrac%7B1%7D%7B2%7D%28%20%28m%2B2n%29%5E2%2B%28m%2B3%29%5E2-%282n%2B1%29%5E2-4%5E2%20%29%3D%5Cdfrac%7B1%7D%7B2%7D%28%20%28m%2B2n%2B2n%2B1%29%28m%2B2n-2n-1%29%2B%28m%2B3%2B4%29%28m%2B3-4%29%20%29%3D%5Cdfrac%7B1%7D%7B2%7D%28%20%28m%2B4n%2B1%29%28m-1%29%2B%28m%2B7%29%28m-1%29%20%29%3D%5Cdfrac%7B1%7D%7B2%7D%28m%2B4n%2B1%2Bm%2B7%29%28m-1%29%3D%28m%2B2n%2B4%29%28m-1%29)
Тогда один из множителей равен ![\pm1](https://tex.z-dn.net/?f=%5Cpm1)
![1) m-1=1=>m=2=>m+2n+4=2n+6=2(n+3)](https://tex.z-dn.net/?f=1%29%20m-1%3D1%3D%3Em%3D2%3D%3Em%2B2n%2B4%3D2n%2B6%3D2%28n%2B3%29)
простое <=> ![n+3=1=>n=-2](https://tex.z-dn.net/?f=n%2B3%3D1%3D%3En%3D-2)
2) ![m-1=-1=>m=0=>m+2n+4=2n+4=2(n+2)](https://tex.z-dn.net/?f=m-1%3D-1%3D%3Em%3D0%3D%3Em%2B2n%2B4%3D2n%2B4%3D2%28n%2B2%29)
простое <=> ![n+2=-1=>n=-3](https://tex.z-dn.net/?f=n%2B2%3D-1%3D%3En%3D-3)
3) ![m+2n+4=1=>m-1=-2n-4=2(-n-2)](https://tex.z-dn.net/?f=m%2B2n%2B4%3D1%3D%3Em-1%3D-2n-4%3D2%28-n-2%29)
простое <=>
простое <=> ![-n-2=1=>-n=3=>n=-3=>m=1-4+6=3](https://tex.z-dn.net/?f=-n-2%3D1%3D%3E-n%3D3%3D%3En%3D-3%3D%3Em%3D1-4%2B6%3D3)
4) ![m+2n+4=-1=>m-1=-2n-6=2(-n-3)](https://tex.z-dn.net/?f=m%2B2n%2B4%3D-1%3D%3Em-1%3D-2n-6%3D2%28-n-3%29)
простое <=> ![n+3=1=>n=-2=>m=-1-4+4=-1](https://tex.z-dn.net/?f=n%2B3%3D1%3D%3En%3D-2%3D%3Em%3D-1-4%2B4%3D-1)
Ответ: (2;-2), (0;-3), (3;-3), (-1;-2)
В скобках получиться 93:5=18,6-3*4=6,6+7=13,6
45 сек=1/80часа: 600м=0,6км: х - длина платформы
(0,6+х)/70=1/80
48+80х=70
х=22/80
х=0,275км=<u>275м</u>