Dạng 2:
Bài 1:
$a) \dfrac{5xy-4y}{2x^{2}y^{3}}+\dfrac{3xy+4y}{2x^{2}+y^{3}}\\=\dfrac{y(5x-4)}{2x^{2}y^{3}}+\dfrac{y(3x+4)}{2x^{2}y^{3}}\\=\dfrac{5x-4}{2x^{2}y^{2}}+\dfrac{3x+4}{2x^{2}y^{2}}\\=\dfrac{5x-4+3x+4}{2x^{2}y^{2}}\\=\dfrac{8x}{2x^{2}y^{2}}\\=\dfrac{4}{xy^{2}}\\c)\dfrac{3}{2x+6}-\dfrac{x-6}{2x^{2}+6x}\\=\dfrac{3}{2(x+3)}-\dfrac{x-6}{2x(x+3)}\\=\dfrac{3x-(x-6)}{2x(x+3)}\\=\dfrac{3x-x+6}{2x(x+3)}\\=\dfrac{2x+6}{2x(x+3)}\\=\dfrac{2(x+3)}{2x(x+3)}\\=\dfrac{1}{x}\\d) \dfrac{2x}{x^{2}+2xy}+\dfrac{y}{xy-2y^{2}}+\dfrac{4}{x^{2}-4y^{2}}\\=\dfrac{2x}{x(x+2y)}+\dfrac{y}{y(x-2y)}+\dfrac{4}{(x-2y)(x+2y)}\\=\dfrac{2}{x+2y}+\dfrac{1}{x-2y}+\dfrac{4}{(x-2y)(x+2y)}\\=\dfrac{2(x-2y)+x+2y+4}{(x-2y)(x+2y)}\\=\dfrac{2x-4y+x+2y+4}{x^{2}-4y^{2}}\\=\dfrac{3x-2y+4}{x^{2}-4y^{2}}\\e) \dfrac{15x}{7y^{3}}.\dfrac{2y^{2}}{x^{2}}=\dfrac{15}{7y}.\dfrac{2}{x}=\dfrac{30}{7xy}$
