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Calculați, aplicând regulile de calcul cu puteri:a)[(4/7)^2×(4/7)^3]^4÷(4/7)^13; b)[9/5×(9/5)^12]^3÷(9/5)^10; c)(3/7)^40÷[(3/7)^3)×(3/7)^5]^2.​