=xy[x^2-y^2][x+y]
=xy[x+y]^2[x-y]
Second, multiple-choice questions:
1, given 2x 2-3xy+y 2 = 0 (xy ≠ 0), the value of x/y+y/x is
2 . 3/2
b、2
two-thirds
d、9
[2x-y][x-y]=0
y=2x，x/y+y/x=5/2
y=x，x/y+y/x=2
2. Given that A 2+B 2+C 2-2 (A+B+C)+3 = 0, the value of A 3+B 3+C 3-3 ABC is
Answer, 0
b 、-3
c、3
d、9
a^2+b^2+c^2-2(a+b+c)+3=0
a^2+b^2+c^2-2a-2b-2c+3=0
a^2-2a+ 1+b^2-2b+ 1+c^2-2c+ 1=0
(a- 1)^2+(b- 1)^2+(c- 1)^2=0
a= 1，b= 1，c= 1
a^3+b^3+c^3-3abc=0
Option: a
3. It is known that the speed of a car from A to B is V 1 and the speed of returning from B to A is V2, so the original average speed of this car is
a 、( V 1+V2)/2
b 、( V 1+V2)/V 1V2
c、V 1V2/(V 1+V2)
d、2V 1V2/(V 1+V2)
2s/[s/v 1+s/v2]= 2v 1 v2/[v 1+v2]
Option: d
3. Calculation:1/x+1/2x+1/3x =?
=[6+3+2]/6x
= 1 1/6x