1提示:(1)x=1.(2)x=4/5. (3)x=-3. (4)x=-2.
2.提示:(1)x=1. (2)y=-8/3. (3)x=21. (4)x=-10. (5)x=0. (6)x=-1/2.
3.提示:(1)x=2. (2)x=1. (3)x=1/2. (4)x=5/8.
4.解:由题意得5(x+2)=2(2x+7),去括号,得5x+10=4x+14,移项,得5x-4x=14-10,合并同类型,得x=4.
5.解:将a=12,h=8,s=120代入S=1/2(a+b)h,得1/2(12+b)×8=120,即12+b=30,b=18.
6.提示:(1)x=4. (2)x=10. (3)x=-3/2. (4)x= 7/9.
7.解:(1)由题意得x+3=2-x,即2x=-1,x=-1/2,即当x=-1/2 时,y_1=y_2.
(2)由题意得(x+3)-2(2-x)=5,去括号,得x+3-4+2x=5,移项,合并同类项,得3x=6,解得x=2,即当x=2时,y_1 比2_y2大5.