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determinati opusul numerelor. a=5+7+9.......+81

Răspuns :

[tex]a = 5 + 7 + 9 + ... + 81[/tex]

[tex]r = 2[/tex]

[tex]a = \frac{81 - 5}{2} + 1 = \frac{76}{2} + 1 = 38 + 1 = 39[/tex]

[tex]-a=-39[/tex]