9.
a, 4x+12=-7x+17
     11x=5
     x=5/11

9) a) 4(x+3)  =-7x+17
<=> 4x+12 +7x -17=0
<=> 11x -5=0
<=> 11x=5
<=> x=5/11
 b) (x+5)(2x-1) = (2x-3)(x+1)
<=> 2x^2 -x +10x -5 = 2x^2 +2x -3x -3
<=> 2x^2 -2x^2 -x+10x -2x+3x = 5-3
<=> 12x = 2
<=> x=2/12
<=> x=1/6
c) (x+3)^2 - (x-3)^2 = 6x+18
<=> x^2+6x +9 -(x^2 -6x +9) -6x -18=0
<=> x^2 +6x +9 - x^2 +6x -9 -6x-18=0
<=> 6x=18
<=> x=3
10) a) [3(5x-2)]/4  -2 = (7x)/3 -5(x-7)
<=> [9(5x-2)]/12 - 24/12  = (28x)/12 - [60(x-7)]/12
=> 9(5x-2) -24= 28x -60(x-7)
<=> 40x -18 -24 =28x -60x +420
<=> 40x -28x +60x = 18+24 +420
<=> 72x = 462 
<=> x= 77/12 
b)(2x-1)/5 -(x-2)/3 = (x+7)/15
=> 3(2x-1) - 5(x-2) = x+7
<=> 6x -3 -5x +10=x+7
<=> 6x -5x-x=-10+3+7
<=> 0x =0
=> pt có vô số nghiệm
c) (x+29)/31 + (x+27)/33 = (x+17)/43 + (x+15)/45
<=> (x+29)/31 +1 (x+27)/33 +1 =(x+27)/43 +1 (x+15)/45 +1
<=> (x+60)/31 + (x+60)/33 = (x+60)/43 + (x+60)/45
<=> (x+60)/31 + (x+60)/33-(x+60)/43 -(x+60)/45=0
<=> (x+60)/(1/31 + 1/33 -1/43 -1/45)=0
<=> x+60=0
<=> x=-60
 d) (1909-x)/91 + (1907-x)/93 + (1905-x)/95 + (1903-x)/97 +4=0
<=> (1909-x)/91 + 1 + (1907-x)/93 + 1 + (1905-x)/95 +1 + (1903-x)/97 + [4(2000-x)]/(2000-x) =0
<=> (2000-x)/91 + (2000-x)/93 + (2000-x)/95 + (2000-x)/97 + [4(2000-x)]/(2000-x)=0
<=> (2000-x) (1/91 +1/93+1/95+1/97 +4/(2000-x))=0
<=> 2000-x=0
<=> x=2000