Toán 8

V

vipboycodon

Bài 2 :
$B = \dfrac{3x-2y}{3x+2y}$
$B^2 = \dfrac{9x^2-12xy+4y^2}{9x^2+12xy+4y^2}$
$B^2 = \dfrac{8xy}{32xy} = \dfrac{1}{4}$
=> $B = \dfrac{1}{2}$
 
N

ngocbich74

Bài 1
3x-y+2x+y=3z+7z

\Rightarrow5x=10z\Rightarrowx=2z

Mà 3x-y=3zhay 6z-y=3z\Rightarrowy=3z

Thay x=2z,y=3zvào biểu thức ta có

C=$\dfrac{(2z)^2-2.2z.3z}{(2z)^2+(3z)^2}$=......=$\dfrac{8}{13}$
 
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