1、x²+ax+b,当x=2时,4+2a+b=3,b=-1-2a;当x=-3时,9-3a+b=4,b=-5+3a
-1-2a=-5+3a
a=4/5
b=-13/5
a-b=4/5+13/5=9/5
2、3x+y-z=0,z=3x+y
代入x+2y-4z=0得x+2y-12x-4y=0
-11x=2y
x=-2y/11
z=3x+y
=-6y/11+y
=5y/11
x:y:z=-2y/11:y:5y/11
=-2/11:1:5/11
=-2:11:5
3、设用于做桌面的木料为X立方,用于做桌腿的为Y立方.
X+Y=5 ,X=5-Y
300Y=4(30X)=120X
2X=5Y
2(5-Y)=5Y
Y=10/7
X=25/7
4、x/2+y/3=2
化简为3x+2y=12
两边同时乘3:9x+6y=36 (1)
2x+3y=28
两边同时乘2:4x+6y=56 (2)
(1)-(2):5x=-20
x=-4
y=12