[tex]\displaystyle\bf\\\text{\bf Toate problemele de pe pagina asta se rezolva in N.}\\4)\\x=1+3+5+7+...+ 1999\\\\Calculam~numarul~de~termeni:\\\\n=\frac{1999-1}{2}+1=\frac{1998}{2}+1=999+1=1000~de~termeni\\x=1+3+5+7+...+ 1999=\frac{1000(1999+1)}{2}=\\\\=\frac{1000\cdot2000}{2}=1000\cdot1000=1000^2=\boxed{\bf1.000.000}\\\\\\5)\\x=2(1+2+3+4+...+80)-6399\\\\x=2\cdot\frac{80\cdot81}{2}-6399\\\\ x=80\cdot81-6399\\x=6480-6399\\x=81\\\sqrt{x}=\sqrt{81}=\boxed{\bf9}[/tex]
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[tex]\displaystyle\bf\\6)\\a=\sqrt{\Big(-2\Big)^4\Big(-3\Big)^6\Big(-7\Big)^2\Big(-11\Big)^2}\\\\Toate~puterile~sunt~pare.\\\text{Un numar negativ ridicat la o putere para devine un numar pozitiv}\\\\a=\sqrt{2^4\cdot3^6\cdot7^2\cdot11^2}\\\\a=2^2\cdot3^3\cdot7\cdot11\\\\a=4\cdot9\cdot7\cdot11\\\\\boxed{\bf~a=2772}[/tex]
