Question

помогите пожалуйста с 5ым номером

Answer 1

$frac{21-5y}{y^2-9}- frac{y}{y^2-9}: frac{y}{y+3}-frac{y-3}{y+3} = -1\ \ 1)frac{y}{y^2-9}: frac{y}{y+3}=frac{y}{(y-3)(y+3)}* frac{(y+3)}{y}= frac{1}{y-3} \ \ 2) frac{21-5y}{y^2-9}- frac{1}{y-3} -frac{y-3}{y+3}= frac{21-5y-1(y+3)-(y-3)(y-3)}{(y-3)(y+3)}= \ \ = frac{21-5y-y-3-(y-3)^2}{(y-3)(y+3)}=frac{21-5y-y-3-(y^2-6y+9)}{(y-3)(y+3)}= \ \ =frac{21-5y-y-3-y^2+6y-9}{(y-3)(y+3)}=frac{9-y^2}{(y-3)(y+3)}=frac{-(y^2-9)}{(y-3)(y+3)}=frac{-(y-3)(y+3)}{(y-3)(y+3)}=-1$