Toán Lớp 8: a) $\frac{5x}{x+5}$+$\frac{10}{x+5}$ b)$\frac{4x}{2x+3}$+$\frac{6}{2x+3}$ c)$\frac{9x}{x+3}$+ $\frac{27}{x+3}$ d) $\frac{20}{x+10}$+

TRẢ LỜI

1. a, $\dfrac{5x}{x+5}$ + $\dfrac{10}{x+5}$ 

   = $\dfrac{5x + 10}{x + 5}$

   b, $\dfrac{4x}{2x+3}$ + $\dfrac{6}{2x+3}$

   = $\dfrac{4x+6}{2x+3}$

   = $\dfrac{2(2x+3)}{2x+3}$

   $\text{= 2}$

   c, $\dfrac{9x}{x+3}$ + $\dfrac{27}{x+3}$

   = $\dfrac{9x+27}{x+3}$

   = $\dfrac{9 ( x + 3 ) }{x+3}$

   $\text{= 9}$

   d, $\dfrac{20}{x +10}$ + $\dfrac{2x}{x +10}$

   = $\dfrac{20 + 2x}{x + 10}$

   = $\dfrac{2 (  10 + x ) }{x+10}$

   $\text{= 2 }$

   e, $\dfrac{1}{x + 4}$ + $\dfrac{3}{x – 2}$

    = $\dfrac{ x – 2 + 3 ( x + 4 ) }{ ( x + 4 )( x – 2 ) }$

    = $\dfrac{ 4x + 10 }{( x + 4 )( x – 2 )}$

   f, $\dfrac{3}{x + 2}$ + $\dfrac{4}{x – 5}$

    = $\dfrac{ 3x – 15 + 4x + 8}{( x + 2 )( x – 5 )}$

    = $\dfrac{ 7x – 7 }{ ( x + 2 )( x – 5 )}$

   g, $\dfrac{2}{x + 6}$ + $\dfrac{1}{x – 4}$

    = $\dfrac{ 2x – 8 + x + 6 }{ ( x + 6 )( x – 4 )}$

    = $\dfrac{ 3x – 2 }{ ( x + 6 )( x – 4 ) }$

   h, $\dfrac{8}{x + 3}$ + $\dfrac{6}{x – 2}$

   = $\dfrac{8x -16 + 6x + 18}{ ( x + 3 )( x – 2 )}$

   = $\dfrac{14x + 2 }{( x + 3 )( x – 2 )}$

   Trả lời