Question

Cho x-y=9 tính B \(=\frac{4x-9}{3x+y}-\frac{4x+9}{3y+x}\)

Answer 1

  B=(4x-9)/(3x+y)-(4y+9)/(3y+x) 
= [4x-(x-y)]/(3x+y) - [4y+(x-y)]/(3y+x) 
= (4x-x+y)/(3x+y) - (4y+x-y)/(3y+x) 
= (3x+y)/(3x+y) - (3y+x)/(3y+x) 
= 1 - 1 = 0

Answer 2

x - y = 9

=> x = 9 + y

=> B = \(\frac{4.\left(9+y\right)-9}{3.\left(9+y\right)+y}-\frac{4.y+9}{3.y+\left(9+y\right)}=\frac{36+4y-9}{27+3y+y}-\frac{4y+9}{4y+9}=\frac{27+4y}{27+4y}-1=1-1=0\)

Answer 3

Mình tưởng là \(B=\frac{4x-9}{3x+y}-\frac{4y+9}{3y+x}\)chứ nhỉ (vòng 11 violympic phải không bạn?)