Question

1+2+3+....+19+20 $.$
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Answer 1

Após resolver os cálculos, concluímos que o valor da soma 1+2+3+....+19+20 é:

$\large\displaystyle\text{ \boxed{\boxed{\bf{ 210 }}} }$

fórmula:

$\large\displaystyle\text{ \mathsf{S_n = \dfrac{ (a_1 + a_n) \cdot{n} }{2}} }$

Onde:

$\large\displaystyle\text{ \mathsf{ \begin{cases} \sf a_1 = 1 \\ \sf a_n = 20 \\ \sf n = 20\end{cases}} }$

Temos que:

$\large\displaystyle\text{ \mathsf{S_{20} = \dfrac{(1 + 20) \cdot20}{2} } }$

$\large\displaystyle\text{ \mathsf{S_{20} = \dfrac{21 \cdot20}{2} } }$

$\large\displaystyle\text{ \mathsf{S_{20} = \dfrac{420}{2} } }$

$\large\displaystyle\text{ \boxed{ \boxed{\mathsf{S_{20} = 210}} } }$