[x/(x-y) + 2xy/(x^2-2xy+y^2)]* {2x/(x+y) - 1} =
= [x/(x-y) + 2xy/(x-y)^2] * [{2x -(x+y)} / (x+y)] =
= [ {x(x-y)+2xy} / (x-y)^2] * [(x-y)/(x+y)] =
= [(x^2-xy+2xy) / (x-y)^2 * [(x-y)/(x+y)]
= [(x^2+xy)] / [(x-y)(x+y)]=
= x(x+y) / [(x-y)(x+y)]=
=x / (x-y) = (-2) / (-2+1) = (-2)/(-1) = 2
Решение смотри в приложении
2)(2n²+11n+14)/(n+3) - 2n + 1/(n+3)=(2n²+11n+15)/(n+3) -2n=
=(2n²+11n+15-2n²-6n)/(n+3)=(5n+15)/(n+3)=
=5(n+3)/(n+3)=5, n≠-3
4)3ˇ(10x+5)-1≥0
3ˇ(10x+5)≥1
3ˇ(10x+5)≥3ˇ0
10x+5≥0
10x≥-5
x≥-1/2
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х - количество 50-рублёвых купюр, у - количество 10-рублёвых купюр.