$bài 1$
$a/$
$ta có:$
-(49-3x)+41=-49+3x+41=3x-8(đpcm)
$b/$
-(a+b+c+1)+(b-c)-(a-c-1)=-a-b-c-1+b-c-a+c+1=-2a-c(đpcm)
$bài 2:$
$x.y=-7$
$ta có:$
$-7=1(-7)=(-7).1$
$vì x<y nên ⇒x.y=-7=(-7).1$
$+)x.y=(-7).1⇔$\left \{ {{x=-7} \atop {y=1}} \right.$ $
$vậy (x;y)={(-7;1)}$