Question

determine o 80° termo da P.A (2,8,14,....​

Answer 1

resolução!

r = a2 - a1

r = 8 - 2

r = 6

a80 = a1 + 79r

a80 = 2 + 79 * 6

a80 = 2 + 474

a80 = 476

Sn = ( a1 + an ) n / 2

Sn = ( 2 + 476 ) 80 / 2

Sn = 478 * 40

Sn = 19120

Answer 2

$\large\boxed{\boxed{{a_{n}=a_{1}+(n-1)*r}}}}}$

$Onde:\left\{\begin{array}{cc}a_{1}=2\\r=a_{2}-a_{1}\\r=8-2=6\\n=80\\a_{n}=a_{80}=?\\\end{array}\right$

$\Leftrightarrow\:a_{80}=2+(80-1)*r$

$\Leftrightarrow\:a_{80}=2+80r-r$

$\Leftrightarrow\:a_{80}=2+79r$

$\Leftrightarrow\:a_{80}=2+79*6$

$\Leftrightarrow\:a_{80}=2+474$

${\color{blue}{\Leftrightarrow\:a_{80}=476}}$

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