Question

ache a soma dos termos da p.a (33,36,...,345)

Answer 1

Boa noite!

Dados;

A1 → 33

N → ?

An → 345

R → a2-a1 → 36-33 = 3

__________________

An=a1+(n-1)·r

345=33+(n-1)·3

345=33+3n-3

-3n=33-3-345

-3n=30-345

-3n=-315

n=-315/-3

n=105

______________

$\textit{Sn}=\frac{\mathrm{(A1+An).n}}{\mathrm{2}}$

$\textit{S105}=\frac{\mathrm{(33+345).105}}{\mathrm{2}}$

$\textit{S105}=\frac{\mathrm{378.105}}{\mathrm{2}}$

$\textit{S105}=\frac{\mathrm{39690}}{\mathrm{2}}$

$\mathbf{S105}=\boxed{19845}$

Att;Guilherme Lima

Answer 2

Resolução!


r = a2 - a1

r = 36 - 33

r = 3



an = a1 + ( n - 1 ) r

345 = 33 + ( n - 1 ) 3

345 = 33 + 3n - 3

345 = 30 + 3n

345 - 30 = 3n

315 = 3n

n = 315 / 3

n = 105


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Sn = ( a1 + an ) n / 2

Sn = ( 33 + 345 ) 105 / 2

Sn = 378 * 105 / 2

Sn = 39690 / 2

Sn = 19.845




espero ter ajudado