Bài 1:
a) -3x + 27 = 0
<=> -3x = -27
<=> x=-27/-3
<=> x= 9
Vậy S = (9)
b) 40/(18+x) + 40/(18-x)=9/2
<=> 40/(18+x) + 40/(18-x) - 9/2 = 0
<=> 80(18-x) + 80(18+x) * (18-x) / 2*(18+x)*(18-x) = 0
<=> 80(18-x) + 80(18+x) * (18-x) =0
<=> 1440 - 80x + 1440 + 80x - 9*( 324- x*x) =0
<=> 1440 +1440 - 2916 + 9*x*x = 0
<=>-36 + 9*x*x =0
<=> 9*x*x = 36
<=> x*x = 4
<=> x=2: x=-2
Vậy S=(2:-2)
c) (2x -7)*(2x-7) - 6*(2x-7)*(x-3)=0
<=> (2x-7) * ( 2x-7-6x+18) =0
<=> (2x-7)*(-4x+11)=0
=> 2x-7=0 hoặc -4x+11 =0
=> x=7/2 hoặc x=11/4
Vậy S=(7/2;11/4)
d) ( viết lại đề)
<=> x-3 - (2*x*x -11x + 15)/6 = -(x-3) mũ 2/4
<=> x-3 - (2*x*x -11x +15) /6 = ( x*x -6x +9)/4
<=> 34x -66 -4*x*x + 3*x*x + 18x -27
<=> 34x -66-4*x*x + 3*x*x -18x + 27=0
<=> 16-39 -x*x =0
<=> x*x -16x + 39=0
<=> x*x - 3x -13x + 39 =0
<=> x*(x-3)*(x-13)=0
<=> ( x-3)*(x-13)=0
=> x-3=0 hoặc x-13=0
=> x=3 hoặc x=13
Vậy S=(3;13)
