Toán Lớp 8: h) $\frac{x – 2}{2x – 2y}$ – $\frac{x-y}{2x + 2y}$ – $\frac{2y^2}{y^2 – x^2}$
i) $\frac{1 +x}{x – 3}$ – $\frac{1-2x}{3+x}$ – $\frac{x (1 -x)}{9 -x^2}$
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Toán Lớp 8: h) $\frac{x – 2}{2x – 2y}$ – $\frac{x-y}{2x + 2y}$ – $\frac{2y^2}{y^2 – x^2}$
i) $\frac{1 +x}{x – 3}$ – $\frac{1-2x}{3+x}$ – $\frac{x (1 -x)}{9 -x^2}$
Comments ( 1 )
MC: 2(x+y)(x-y)
= {(x+y)(x-2)}/{2(x-y)(x+y)} – {(x-y)^2}/{2(x-y)(x+y)} + {2y^2 . 2}/{2(x+y)(x-y)}
= {3y^2 + 3xy -2x – 2y}/{2(x+y)(x-y)}
= {(x+y)(3y-2)}/{2(x+y)(x-y)}
= {3y-2}/{2(x-y)}
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i, {1+x}/{x-3} – {1-2x}/{3+x} – {x(1-x)}/{9-x^2}
MC: (x-3)(x+3)
= { 4x + x^2 + 3 – 5x + 2x^2 – 3 + x – x^2 }/{(x-3)(x+3)}
= {2x^2}/{(x-3)(x+3)}