Question

初二数学题关于乘法公式2道

1. x2+y2=25,x+y=7,且x大于y，求x-y的值2. 已知x2+y2-6x+10y+34=0，求x+y的值 不光要答案，还要具体的过程，先给5分，好的再加

Answer 1

1.(x+y)^2=49 xy=12 (x-y)^2=x^2+y^2-2xy=25-24=1 x-y=1(x>y)
2.(x-3)^2+(y+5)^2-9-25+34=0 .(x-3)^2+(y+5)^2=0 .(x-3)^2=0且(y+5)^2=0 X=3 Y=-5
X+Y=-2

Answer 2

1、
X^2+Y^2=25
X+Y=7
(X+Y)^2=X^2+Y^2+2XY
49=25+2XY
XY=12
(X-Y)^2=X^2+Y^2-2XY=25-24=1 且X大于Y
X-Y=1
X+Y=7
X=4，Y=3
2、

Answer 3

1.(x+y)^2=x^2+y^2+2xy
49=25+2xy
2xy=24
（x-y）^2=(x+y)^2-4xy
(x-y)^2=49-48
(x-y)^2=1
x大于y
x-y=1
2. x^2-6x+9+y^2+10y+25=0
(x-3)^2+(y+5)^2=0
x=3, y=-5
x+y=3-5=2