设0≤a

设0≤a 设0≤a 设0≤a 设0≤a 设1≤a 设a>0,0 设a>0,0 设a>0,0 设a>0,0 设0＜a 设0〈a 设a>1,0 设a>1,0 设a>0,b 设a>0,b 设a设a 设A={-2≤x ≤a,0 设a为实数,0