过A点作BC的垂线交BC于E,显然△MPB∽△AEB
有MP/AP=BP/BE,即MP=AP*BP/BE=6*(8-x)/(8-3)=6(8-x)/5
S=MN*MP=6(8-x)x/5=-6/5*(x-4)²+6*16/5
当MN=x=4时,S有最大值19.2cm²
过A点作BC的垂线交BC于E,显然△MPB∽△AEB
有MP/AP=BP/BE,即MP=AP*BP/BE=6*(8-x)/(8-3)=6(8-x)/5
S=MN*MP=6(8-x)x/5=-6/5*(x-4)²+6*16/5
当MN=x=4时,S有最大值19.2cm²