Chứng minh các đẳng thức sau : `a). {x-2}/-x={2^3-x^3}/{x(x^2+2x+4x)}` $(x\ne0)$ `b). {3x}/{x+y}={-3x(x-y)}/{y^2-x^2}` $x\ne

2 bình luận về “Chứng minh các đẳng thức sau : `a). {x-2}/-x={2^3-x^3}/{x(x^2+2x+4x)}` $(x\ne0)$ `b). {3x}/{x+y}={-3x(x-y)}/{y^2-x^2}` $x\ne”

1. a)(2^3-x^3)/(x(x^2+2x+4))

   =((2-x)(x^2+2x+4))/(x(x^2+2x+4))

   =(2-x)/x

   =(-(2-x))/(-x)

   =(x-2)/(-x)

   b)(-3x(x-y))/(y^2-x^2)

   =(-3x(x-y))/((y-x)(x+y))

   =(-[-3x(x-y)])/(-(y-x)(x+y))

   =(3x(x-y))/((x-y)(x+y))

   =(3x)/(x+y)

   c)(3a(x+y)^2)/(9a^2 (x+y))

   =(3a.(x+y).(x+y))/(3a.(x+y).3a)

   =(x+y)/(3a)

   Trả lời
2. a)VP=(2^3-x^3)/((x(x^2+2x+4))   (xne0)

   =(x^3-2^3)/(-x(x^2+2x+4))

   =((x-2)(x^2+2x+4))/(-x(x^2+2x+4))

   =(x-2)/(-x)=VT(đpcm) 

   b)VP=(-3x(x-y))/(y^2-x^2)(xne+-y)

   =(3x(y-x))/((y-x)(y+x))

   =(3x)/(y+x)

   =(3x)/(x+y)=VT(đpcm)

   c)VP=(3a(x+y)^2)/(9a^2(x+y))(ane0;xne-y)

   =(3a(x+y)^2)/((3a)^2(x+y))

   =(x+y)/(3a)=VT(đpcm)

   @yn

   Trả lời