Đáp án:
Giải thích các bước giải:
c) đặt 1/x=a ; 1/y= b
$\left \{ {{a+5b=-5} \atop {3a+2b=11}} \right.$ <=>$\left \{ {{3a+15b=-15} \atop {3a+2b=11}} \right.$ <=>$\left \{ {{13b=-26} \atop {a=-5-5b}} \right.$<=> $\left \{ {{a=5} \atop {b=-2}} \right.$
=>1/x=5=>x=1/5 ; 1/y=-2 => y=-1/2
d) Đặt 1/x+2=a; 1/y-1 = b
<=>$\left \{ {{a+b=2} \atop {2a-3b=1}} \right.$ <=>$\left \{ {{2a+2b=4} \atop {2a-3b=1}} \right.$ <=>$\left \{ {{5b=3} \atop {a=2-b}} \right.$ <=>$\left \{ {{b=3/5} \atop {a=7/5}} \right.$
=>1/x+2=7/5<=>x+2=5/7 <=>x=-9/7
=>1/y-1=3/5<=>y-1=5/3<=>y=8/5
