Cho ab\dfrac{a}{b}=cd\dfrac{c}{d} chứng minh rằng:

a) aab\dfrac{a}{a-b}=ccd\dfrac{c}{c-d}

b) ab\dfrac{a}{b}=a+cb+d\dfrac{a+c}{b+d}

c)a3a+b\dfrac{a}{3a+b}=c3c+b\dfrac{c}{3c+b}

d) a.cb.c\dfrac{a.c}{b.c}=a2+c2b2+d2\dfrac{a^2+c^2}{b^2+d^2}

e) a.bc.d\dfrac{a.b}{c.d}=a2b2c2d2\dfrac{a^2-b^2}{c^2-d^2}

f) a.bc.d\dfrac{a.b}{c.d}=(ab)2(cd)2\dfrac{\left(a-b\right)^2}{\left(c-d\right)^2}

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