16、解：(1)原式=5y/(x^2)(2)原式=x/(2y) 17、解：最简公分母是(2m+3)(2m-3)，故：2mn/(4m^2 -9)=2mn/[(2m+3)(2m-3)](2m-3)/(2m+3)=(2m-3)^2/[(2m+3)(2m-3)] 满意老师的回答敬请采纳，谢谢
