1.X+3=7-Y
x+y=7-4
x+y=3
∴(x+y)^2-(3/2)^2=55/4
2.8+3a=35
3a=27
a=9
∴8-3a=8-27=-19
3.a+b/2a-b=2
∴2(a+b)=2a-b
3(a+b)/5(2a-b)- 2a-b/3(a+b)
=6/5-1/6
=31/30
4.将a=3带入原式中,
得:9+6+m=0
m=-15
5.x+y=8①,x-y=2②
①+②得:2x=10
x=5
∴y=8-5=3
∴x^2-xy+y^2=25-15+9=19
6.∵a^2-2b-3=0
∴a^2-2b=3
∴2a^2-4b+5
=2(a^2-2b)+5
=2*3+5
=11
7.这题不对吧,条件中没有a
8.3(x+y)^2-4/x+y+2x-3+2y
=3*3^2-4/(x+y)-3+(2x+2y)
=27-4/3-3+6
=86/3