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1) $((\frac{1}{25})^{-1/2}* 7^{-1}-(\frac{1}{8} )^{-1/3}*2^{-2}):49^{-1/2}=\\ =(25^{1/2}*\frac{1}{7}-8^{1/3}*\frac{1}{2^2}):(\frac{1}{49})^{1/2}=(\frac{5}{7}-\frac{2}{4}):\frac{1}{7} =\frac{3}{14}*7=\frac{3}{2}$

2) $\frac{4a^7*b^4}{5c^4*d^3}*\frac{15bc^3}{8a^6*d^2}*\frac{2cd}{3ad} =\frac{4*15*2}{5*8*3}* \frac{a^7}{a^6*a}*\frac{b^4*b}{1}*\frac{c^3*c}{c^4}*\frac{1}{d^3*d^2}=\frac{b^5}{d^5}$

3) $\frac{a-b}{a^{1/3}-b^{1/3}} -\frac{a+b}{a^{1/3}+b^{1/3}} =\frac{(a^{1/3}-b^{1/3})(a^{2/3}+a^{1/3}*b^{1/3}+b^{2/3})}{a^{1/3}-b^{1/3}} -\\ -\frac{(a^{1/3}+b^{1/3})(a^{2/3}-a^{1/3}*b^{1/3}+b^{2/3})}{a^{1/3}+b^{1/3}}=\\ =a^{2/3}+a^{1/3}*b^{1/3}+b^{2/3}-a^{2/3}+a^{1/3}*b^{1/3}-b^{2/3}=2a^{1/3}*b^{1/3}$