=(1998+1+1/1997)*1/1998=(1998+1998/1997)*1/1998=1998*1/1998+1998/1997*1/1998=1+1/1997=1又1/1997
设顶角是x度则底角是(180-x)/2度所以2x=(180-x)/2180-x=4x5x=180x=36答:顶角是36度完全正确412354103564