1,x+8=3
⇔x=-5
Vậy S={5}
2,x-5=-8
⇔x=-3
Vậy S={-3}
3,x+12=5
⇔x=-7
Vậy S={-7}
4,3x-21=0
⇔3x=21
⇔x=7
Vậy S={7}
5,3x-7=2x-3
⇔3x-7-2x+3=0
⇔x-4=0
⇔x=4
Vậy S={4}
6,8x²-4x=0
⇔4x(2x-1)=0
⇔\(\left[ \begin{array}{l}x=0\\x=1/2\end{array} \right.\)
Vậy S={0;1/2}
7,8x-3=5x+12
⇔8x-3-5x-12=0
⇔3x-15=0
⇔3(x-5)=0
⇔x=5
Vậy S={5}
8,9x-11=13-3x
⇔9x-11-13+3x=0
⇔12x-24=0
⇔12(x-2)=0
⇔x=2
Vậy S={2}
9,5x+5=2x+3
⇔5x+5-2x-3=0
⇔3x-2=0
⇔x=2/3
Vậy S={2/3}
10,-4x+5=-5x+6
⇔-4x+5+5x-6=0
⇔x-1=0
⇔x=1
Vậy S={1}
11,x+1=2(x+7)
⇔x+1=2x+14
⇔x+1-2x-14=0
⇔-x-13=0
⇔x=13
Vậy S={13}
12,2x-3=4x+6
⇔2x-3-4x-6=0
⇔-2x-9=0
⇔x=-2/9
Vậy S={-2/9}
13,x(x-1)=-x(x+3)
⇔x²-x=-x²-3x
⇔x²-x+x²+3x=0
⇔2x²+2x=0
⇔2x(x+1)=0
⇔\(\left[ \begin{array}{0}x=0\\x=-1\end{array} \right.\)
Vậy S={0;-1}
14,x-8=3-2(x+4)
⇔x-8=3-2x-8
⇔x-8=-2x-5
⇔x-8+2x+5=0
⇔3x-3=0
⇔x=1
Vậy S={1}
15,90-x=2(120-3x)
⇔90-x=240-6x
⇔90-x-240+6x=0
⇔5x-150=0
⇔5(x-30)=0
⇔x=30
Vậy S={30}
16,2x-3=4x+7
⇔2x-3-4x-7=0
⇔-2x-10=0
⇔-2(x+5)=0
⇔x=-5
Vậy S={-5}
17,2x-3=4x+6
⇔2x-3-4x-6=0
⇔-2x-9=0
⇔x=-9/2
Vậy S={-9/2}
Chúc bạn học tốt nha~
~Cheese~
