7х=4*2,8 х=11,2/7=1,6 х=1,6
<span>(y/x-y + x/x+y) : (1/x^2 + 1/ y^2) - y^4/ x^2-y^2 = (y(x+y)+x(x-y)/(x-y)(x+y))/(x^2+y^2/x^2y^2)-y^4/(x-y)(x+y) = (xy+y^2+x^2-xy/(x-y)(x+y))/(x^2+y^2/x^2y^2)-y^4(x-y)(x+y) = (x^2+y^2/(x-y)(x+y))/(x^2+y^2/x^2y^2)-y^4(x-y)(x+y) = (x^2+y^2)(x^2y^2)/(x^2+y^2)(x-y)(x+y)-y^4/(x-y)(x+y) = x^2y^2/(x-y)(x+y)-y^4/(x-y)(x+y) = x^2y^2-y^4/(x-y)(x+y) = y^2(x^2-y^2)/(x-y)(x+y) = y^2(x-y)(x+y)/(x-y)(x+y) = y^2 </span>
А)y=4x-30
y=4•(-2,5)-30
y=-10-30=-40
y=-40
б)-6=4x-30
4x=-30+6
4x=-24
x=-24:4
x=-6
1)5×35= 175 (руб)-за 5 сыров.
2)200-175=25 (руб)
Ответ:25 рублей даст кассир.