一、用短除法求下列各组的最大公因数56和42是1456=7x2x2x242=7×2x3225和15是15225=5x5x3x315=3x554、72和90是1854=2x3x3x372=2x2x2×3x390=2x3x3x560、90和120是3060=2x2x3x590=2x3x3x5120=2×2x2x3x5