(20+5x)(44-x)=1600 (10+x)(200-10乘1/2x)=640

(20+5x)(44-x)=16005x²-200x+720=0x²-40x+144=0(x-4)(x-36)=0x=4或x=36(10+x)(200-5x)=640(10+x)(40-x)=128x²-30x-272=0x=(15+√497)或x=(15-√497)50+50(1+x)+50(1+x)²=18250(1+x)²+50(1+...