C
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Cho $\dfrac{a}{b}$=$\dfrac{c}{d}$.CMR:
a) $\dfrac{a+2b}{a-2b}$=$\dfrac{c+2d}{c-2d}$
b) $\dfrac{a+2c}{b+2d}$=$\dfrac{a-2c}{b-2d}$
a) $\dfrac{a+2b}{a-2b}$=$\dfrac{c+2d}{c-2d}$
b) $\dfrac{a+2c}{b+2d}$=$\dfrac{a-2c}{b-2d}$