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4 Identifică valoarea lui m din egalitatea dată:
1 + 2 + 3 + 4 + ... + 11 + m= 70 + 2 x 9.​


Răspuns :

 

[tex]\displaystyle\bf\\1 + 2 + 3 + 4 + ... + 11 + m= 70 + 2\times9\\\\\frac{11(11+1)}{2}+m=70+ 2\times9\\\\\frac{11\times12}{2}+m=70+ 2\times9\\\\11\times6+m=70+ 18\\\\66+m=88\\\\m=88-66\\\\\boxed{\bf m=22}[/tex]