推 ssuin : 感謝回答! 01/16 16:26
※ 引述《ssuin (紫色的雨)》之銘言:
: x和y都為整數
: 請問
: (i)
: (5/x)-(4/y)=3
5y - 4x = 3xy, 15y - 12x = 9xy, 9xy + 12x - 15y = 0,
9xy + 12x - 15y - 20 = (3x-5)(3y+4) = -20.
-20拆成(20,-1),(10,-2),(5,-4),(4,-5),(2,-10),(1,-20),(-1,20),(-2,10),
(-4,5),(-5,4),(-10,2),(-20,1)十二組因數, 但前一值加5及後一值減4必須是
3的倍數, 故只有(10,-2),(4,-5),(1,-20),(-2,10),(-5,4),(-20,1)合, 但
(-5,4)這組會使x=y=0不合, 故(x,y) = (5,-2),(3,-3),(2,-8),(1,2),(-5,-1).
: (ii)
: (2/x)+(3/y)=1
: 分別有幾組解?
3x + 2y = xy, xy - 3x - 2y = 0, (x-2)(y-3) = 6.
--
※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 163.22.18.20
※ 文章網址: https://www.ptt.cc/bbs/Math/M.1421396703.A.E6A.html