Question

Выражение
1)(a-2)/(a-1)-(a)/(1-a)
2)(3y+7)/(4-y)+(y+15)/(y-4) ​

Answer 1

$1)$

$\frac{a-2}{a-1}-\frac{a}{1-a}=\frac{a-2}{a-1}+\frac{a}{a-1}=\frac{a-2+a}{a-1}=$

$=\frac{2a-2}{a-1}=\frac{2(a-1)}{a-1}=2$   (при  $a\neq 1$)

$2)$

$\frac{3y+7}{4-y}+\frac{y+15}{y-4}=\frac{3y+7}{4-y}-\frac{y+15}{4-y}=$

$=\frac{3y+7-y-15}{4-y}=\frac{2y-8}{4-y}=- \frac{8-2y}{4-y}=$

$- \frac{2(4-y)}{4-y}=-2$ (при  $y\neq 4$)