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2. Calculați, folosind formulele de calcul prescurtat:
a) ) (2√3+3)(2√3 −3)−(√2 − 1)(√2+1);
b) (3-√6)(3+√6)+(√3-1)(√3+1)-(3-√5)(3+√5);
c) (4-2√5)(4+2√5)+(3√2-5) (3√2+5)-(√6 +√√2)(√6-√2):