Question

这种数学题怎么做来着？ 好像是分解因式啥的

Answer 1

x+y分之xy=3，
xy/(x+y)=3,
xy=3(x+y)
-x+3xy-y分之2x-3xy+2y
=(2x-3xy+2y)/(-x+3xy-y)
=[2x-9(x+y)+2y]/[-x+9(x+y)-y]
=-7(x+y)/8(x+y)
=-7/8'
解：令X+Y=M XY=N 所以XY=3(X+Y) 即 N=3M 分母上-x+3xy-y=-(x+y)+3xy=-m+3n
分子上2x-3xy+2y=2(x+y)-3xy=2m-3n 2m-3n/-m+3n=2m-9m/-m+9m=-7/8
由x+y分之xy=3可得 x+y=xy/3 代入（2x-3xy+2y）/(-x+3xy-y)得
（2x-3xy+2y）/(-x+3xy-y)=[-3xy+2（x+y）]/[3xy-（x+y)]=-7/8
x1 = 3/2 (-1 - Sqrt[5]),
y1 = 3/2 (1 - Sqrt[5]),

x2 = -3/2 + (3 Sqrt[5])/2,
y2 = 3/2 (1 + Sqrt[5]),

x^3+3xy+y^2 = -9/2 (3 + 7 Sqrt[5])
x^3+3xy+y^2 =9/2 (-3 + 7 Sqrt[5])

Answer 2

对。
11、3(x+2)(x+4)
12、4(4x+3)(x-1)
13、(2a+3b)^2
14、a^3-4^3