{ diff(x1, t) = (1*k7*1/16*x1 + (-1)*k7*1/8*x1*x2 + (-1)*k7*1/32*x1^2)/k7,
  diff(x2, t) = (1*k7*1/32*x2 + (-1)*k7*275/3200*x1*x2 + (-1)*k7*1/32*x2^2)/k7 }