✔ 最佳答案
題目是:6/a+4/b=5 求(a,b)的有序數對
Sol
加上a,b為整數
6/a+4/b=5
ab(6/a+4/b)=5ab
6b+4a=5ab
5ab-4a-6b=0
a(5b-4)-(6/5)(5b)=0
5a(5b-4)-6(5b)=0
5a(5b-4)-6(5b-4)=24
(5a-6)(5b-4)=24
24=(2^3)*3有正因數(3+1)*(1+1)=8個
分別為1,2,3,4,6,8,12,24
(1) 5a-6=-24
5a=-18(不合)
(2) 5a-6=-12
5a=-6(不合)
(3) 5a-6=-8
5a=-2(不合)
(4) 5a-6=-6
5a=0(不合)
(5) 5a-6=-4
5a=2(不合)
(6) 5a-6=-3
5a=3(不合)
(7) 5a-6=-2
5a=4(不合)
(8) 5a-6=-1
a=1,b=-4
(a,b)=(1,-4)
(9) 5a-6=24
a=6,b=1(a,b)=(6,1)
(10) 5a-6=12
5a=18(不合)
(11) 5a-6=8
5a=14(不合)
(12) 5a-6=6
5a=12(不合)
(13) 5a-6=4
a=2,b=2
(a,b)=(2,2)
(14) 5a-6=3
5a=9(不合)
(15) 5a-6=2
5a=8(不合)
(16) 5a-6=1
a=1,b=4
5a=7(不合)
So
(a,b)=(1,-4) or (6,1)or (2,2)