(8.) 5/x=4/3x1
5/x=4/3
4x=5×3=15
x=15/4
即三又四分之三.
(9) x+3/4=x/5
x-x/5=-3/4
(4/5)x=-3/4
x=(-3/4)÷(4/5)
=(-3/4)×(5/4)
=-15/16.
(10) 10x=1/x+2
10x^2=1+2x
10x^2-2x-1=0
解得 x=1±√11
(11) 5x+1/5=x/2
5x-x/2=-1/5
(9/2)/x=-1/5
x=(-1/5)÷(9/2)
=-(1/5×(2/9)
=-2/45.
(12) 8+5/4=x/3
x/3=8+5/4
=(8×4)/4+5/4
=32/4+5/4
=37/4.
x=3*37/4
=101/4
即二十五又四分之一.
(13) x+2/4=3x-2/5
3x-x=2/4+2/5
=1/2+2/5
=5/10+4/10
=9/10
2x=9/10
x=(9/10)÷2
=(9/10)×1/2
=9/20.
(14) 3x+2/4-3=5
3x+1/2-3=5
3x+1/2-6/2=5
3x-5/2=5
3x=5+5/2
=10/2+5/2
=15/2
x=(15/2)÷3
=(15/2)×(1/3)
=15/6
=5/2.
即二又二分之一.
(15) 2x-1/3+4=1/2
2x-1/3+12/3=1/2
2x+11/3=1/2
2x=1/2-11/3
=3/6-22/6
=-19/6
x=(-19/6)÷2
=(-19/6)×(1/2)
=-19/12.
即负一又一十二分之七
(17) 3x+1/4-3/2=5
3x+1/4-6/4=5
3x-5/4=5
3x=5+5/4
=25/4
x=(25/4)÷3
=(25/4)×(1/3)
=25/12
即二又一十二分之一
(18) 2x+7/5+1/3=-4
2x+21/15+5/15=-4
2x+26/15=-4
2x=-4-26/15
=-60/15-26/15
=-86/15
x=-(86/15)÷2
=-(86/15)×1/2
=-43/15.
即负三又一十五分之一十三.
(19) 3x+1/2-5=1/4
3x+1/2-10/2=1/4
3x-9/2=1/4
3x=1/4+9/2
=1/4+18/4
=19/4
x=(19/4)÷3
=(19/4)×(1/3)
=19/12.
即一又一十二分之七.
(20) x+3/5+3/2=-2
x+6/10+15/10=-2
x+21/10=-2
x=-2-21/10
=-20/10-21/10
=-41/10.
即负四又十分之一.
