Calculați:

a)
[tex]27 \sqrt{3} - 13 \sqrt{5 } + 21 \sqrt{7} - 3 \sqrt{3} + 5 \sqrt{5} = [/tex]

b)
[tex]12 \sqrt{3} \times \sqrt{2} + 12 \sqrt{5} - 12 \sqrt{6} + 2 = [/tex]
c)
[tex]21 \sqrt{3} \div 7 + 3 \sqrt{15} \times 2 \sqrt{5} - 2 \sqrt{3} = [/tex]
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