1、(4sin a-2cos a)/(5cos a+3sin a)分子分母同除以cos a,得：原式=(4tan a-2)/(5+3tan a)=(12-2)/(5+9)=5/72、sin a*cos a配上分母(sin a)^2+(cos a)^2=1原式=sin a*cos a/[(sin a)^2+(cos a)^2] 分子分母同除以(co...