((а+б)^2-(а-б)^2)*(1/а+1/б) =<span>((a^2 +2ab +b^2) - (a^2 - 2ab +b^2))*(1\a + 1\b)=
</span>(a^2 +2ab +b^2 - a^2 + 2ab - b^2)*(1\a + 1\b)=
4ab * *(1\a + 1\b) =4ab\a + 4ab\b=
4b+4a
если <u /> то
4x(x-1)/(x+3) :2(x-1)= 4x(x-1)/(x+3) *1/2(x-1)= 2x/(x+3)
2*2,5/(2,5+3)= 5/5,5= 10/11