Question

求解数学题（高一的）若正数x,y满足x+y+xy=3,则xy的取值范围是

Answer 1

xy=3-(x+y)

又x+y≥2√(xy)

xy≥3-2√(xy)

设√(xy)=t

t²≥3-2t

t≥1或t≤-3(舍)

t²≥1

所以xy≥1