设a>0,0

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0≤a 设a>0,b 设0≤a 设0≤a 设0≤a 设a>0,b 设a为实数,0 设集合A={0 设0小于等于a 设ab>0,-c/a