设纵向长为x cm 则横向宽为623.7/x cm打印面积=（x-2*2.54）（623.7/x-2*3.17）令f(x)=（x-2*2.54）（623.7/x-2*3.17）则f(x)'=-6.34+3168.96/x^2令f(x)'=0x=22.357约22.36cm623.7/x=27.897约27.90cm
