Question

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

Answer 1

 

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