[Toán 8]rút gọn biểu thức

A

angleofdarkness

$\dfrac{y}{3-y}+\dfrac{y^2+3y}{2y+3}.(\dfrac{y+3}{y^2-3y}-\dfrac{y}{x^2-y^2})$

$=\dfrac{y}{3-y}+\dfrac{y(y+3)}{2y+3}.(\dfrac{y+3}{y(y-3)}-\dfrac{y}{x^2-y^2})$

$=\dfrac{y}{3-y}+\dfrac{y(y+3)}{2y+3}.\dfrac{(y+3)(x^2-y^2)-yy(y-3)}{y(y-3)(x^2-y^2)}$

$=\dfrac{y}{3-y}+\dfrac{y+3}{2y+3}.\dfrac{x^2y-y^3+3x^2-3y^2-y^3+3y^2}{(y-3)(x^2-y^2)}$

$=\dfrac{y}{3-y}+\dfrac{y+3}{2y+3}.\dfrac{x^2y-2y^3+3x^2}{(y-3)(x^2-y^2)}$
 
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